Image Credit: Mark Florence
More Musings of an Energy Nerd
Energy myths are persistent, in spite of the fact that energy experts spend a good deal of time performing debunking duty. Many energy experts collect misguided energy-saving tips as a hobby, and pick the myths apart with the dedication of an 18th-century amateur scientist.
In a previous blog, I presented my own list of ten energy myths. My collection included these old chestnuts:
- Walls have to breathe.
- Caulking the exterior of a house reduces air leakage.
- R-value tests only measure conductive heat flow.
- In-floor radiant heating systems save energy.
Two other myth-collecting hobbyists are Rick Diamond and Mithra Moezzi, researchers at Lawrence Berkeley National Laboratory. They presented their list of energy myths in a paper, “Revealing Myths about People, Energy and Buildings.” Here are some myths they shared:
- Cleaning the refrigerator coils improves refrigerator efficiency. According to Diamond and Moezzi, “A review of measured tests with refrigerators showed that there was no or little evidence of improved efficiency from cleaning the coils (Litt, Megowan, and Meier 1993).”
- Installing foam gaskets in electrical outlets will significantly reduce air infiltration. Diamond and Moezzi write, “The probable origin for this myth — an unusual case where an origin can actually be identified — was a study in the late 1970s that showed that 20% of the air leakage in fifty homes was due to wall outlets (Caffey 1979). Later studies showed leakage values for outlets to be under 1%.”
When it comes to energy myth debunking, Michael Blasnik leads the pack
While many writers have assembled similar lists, one myth debunker stands head-and-shoulders above his peers: Michael Blasnik. A researcher and statistician with a steel-trap mind, Blasnik takes nothing on faith. His approach is always the same: “Show me the data.”
A featured speaker at many conferences, Blasnik has presented different versions of his energy-myths collection over the years.…
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86 Comments
Infiltration
I can't imagine wall outlets account for only 1% of a house's energy loss. A 2"x3" section that essentially a "hole" in the wall can add up. Say 10 outlets on the outside wall of a house is 20" x 30". Thats a big hole.
Tune ups are recommended bi-annually, and are only effective on oil-fired units, where the jets may be able to be tuned and cleaned.
Response to Shane Claflin
Shane,
Concerning wall outlets: there are two factors you fail to consider:
1. The air leakage crack is not 2 inches by 3 inches. If the electrical box had no cover plate, the leakage area would be equal to the area of the crack between the drywall and the box, plus the area of the cracks in the knockouts in the back of the box. That's much less than 2"x3". Adding a cover plate further reduces the area of the leakage cracks.
2. Many (most) electrical boxes are near the neutral pressure plane, where there isn't much leakage unless the weather is windy. Because of the stack effect, most significant leaks are in the basement or attic.
I dunno, some of these are so
I dunno, some of these are so qualified as to be misleading.
Right sized furnace. A 40 year old furnace sized for an uninsulated house could easily be twice as large as needed. SO, yes if you buy a state of the art variable rate furnace to replace it,it does not matter much.... but that accounts for what. 5 or 10 percent of sales? So for 90 to 95 percent of the cases, right sizing is important. A 150k btu furnace 86 percent efficient wastes 21k btu every hour it runs, a 75k 10.5, unless it is somehow a perfect world, that larger furnace is running far more than half as long as the smaller,
Windows don't save money.
First assumption is that the new windows leak as much air as the old.
Second is that the new windows have worse solar heat gain than the old windows.
Third is that there is any solar gain to be had at all.
Since in a normal house half the heat goes out the windows[not including leakage] If find this a particularly troubling opinion.
The other factor in place with oversized (even 92-97% eff) furnaces that I’ve noticed as an HVAC tech is that the hotter discharge air temperatures that result from having a huge heat exchanger relative to duct size cook the thermostat and result in short cycling. All the surfaces and objects stay well below the air temp and people are uncomfortable so they bump up the heat.
The way they are typically designed (with a central Thermostat) results in energy wastes too. The thermostat cooks from the 140deg air coming out of the registers in the living room and the upstairs bedroom doesn’t heat sufficiently so the homeowner gets up and bumps up the thermostat.
I see what they mean about low standby losses but in the real world, unless the homeowner is savy, they’re probably gonna waste energy with an oversized furnace. IMHO.
Electrical outlet leakage
A good energy rater told me a typical electrical opening in an outside wall will show 7 to 10 cfm at 50 Pascals.
Response to Keith Gustafson
Keith,
Michael Blasnik just sent me an e-mail; he's busy this morning and won't be able to post any comments here until this afternoon at the earliest. So I'll take a first crack at responding to your question. I imagine that Michael will also be interested in chiming in later.
1. First of all, your estimate of the market penetration of high-efficiency furnaces (with efficiencies over 90% AFUE) is much too low. In some markets like Wisconsin, 85% of all residential furnaces sold are high-efficiency units. While the market penetration in other areas of the country is lower, most cold-climate regions have moved to high-efficiency furnaces.
2. Just because an oversized furnace runs for fewer hours per day than a right-sized furnace does not mean that significant energy is being wasted. It seems you are confusing an argument in favor of high-efficiency furnaces (versus low-efficiency furnaces) with the argument over whether oversized furnaces waste energy compared to right-sized furnaces.
3. Neither Michael Blasnik nor I ever said that "Windows don't save money." Obviously, the replacement of old single-glazed windows with new double-glazed units save energy. The question is, is the investment cost-effective? The answer is no.
4. I can assure you that the many researchers who have run the cost-effectiveness numbers on window replacement jobs have taken air leakage rates into account.
5. It is undeniable that when you replace an existing single-glazed window with a new double-glazed window, the new window will have a lower SHGC than the old window.
6. It is extremely rare to have a house in which all windows were so shaded that SHGC was irrelevant. Perhaps if every single side of a single-story house had deep porches, your scenario might occur. That almost never happens.
7. Your statement, "in a normal house half the heat goes out the windows," is meaningless. What's a normal house? In any case, even in a house in which half the heat loss is attributable to the windows, window replacement isn't cost-effective.
Response to Doug McEvers
Doug,
You wrote, "A good energy rater told me a typical electrical opening in an outside wall will show 7 to 10 cfm at 50 Pascals."
As any good home-performance contractor can tell you, with air leaks in a building, it's all about "Location, location, location." Air leakage during a blower-door test differs greatly from stack-effect air leakage.
It's all about the basement, the crawl space, and the attic.
All in all - good stuff!
Can anyone explain how this is possible? It would seem to me that blocked coils would cause the condenser and fan to have to run longer. Supply data, if possible.
This one hinges on the word "significant." 2 to 3% still puts (keeps) money in my pocket.
A reason I think this one hits the energy saving lists so often, is that the skills required to implement this improvement are well within the range of the "I have a hammer and two screwdrivers in my toolkit crowd." Air sealing the attic, for example, may be beyond their skillset. My take is that the average Joe should caulk and weatherstrip what they can easily manage and then move on to other improvements.
I think that Michael Blasnik is comparing, for example, installing a new 70,000 BTU/hr furnace vs a new 90,000 BTU/hr furnace when the design load may be 65,000 BTU/hr. Comparing a 40-YO furnace to a new furnace just isn't fair. :-)
For me, I'd go with the smaller, but adequate furnace AND tight ducts AND partially closing (one or two) vents for my home. I believe that the issue here is that the "typical California house ... duct leakage" allows so much duct leakage that closing ducts REALLY hurts. I believe that by tightening the ducts, along with not pounding air 90,000 BTU/hr of air through (likely) inadequate ducts you could produce savings by placing more of the heat where it's needed.
P.S. I just read through MB's slides and note especially "not recommended... with ducts located outside of conditioned space."
Response to D. Brown
D. Brown,
Here is a link to a Home Energy article that provides more information to answer your question about dirty refrigerator coils: http://www.homeenergy.org/show/article/nav/appliances/page/15/id/914
I think it's fair to say that the research shows that refrigerator coils are able to dissipate heat even when there is fluff on them. Evidently the fluff does not significantly affect the heat transfer rate.
Comments from Pat Murphy
[Editor's note: Pat Murphy sent me an e-mail asking me to post the following comments:]
You quote Michael as saying that window replacement savings are often overestimated. Agreed.
Then you say window replacement is not cost-effective. What does that mean? Not as cost effective as what? Caulking? Adding insulation? Other??
You acknowledge they save energy. Are you saying that the cost of the windows will always be higher than the savings in energy bills over the lifetime of the window? Are you also implying that the embodied energy in the windows will always be higher than the operating energy over the lifetime of the window? In all climates?
-- Pat Murphy
Response to Pat Murphy
Pat,
When an energy expert says that window replacement is not cost-effective, that means that in all U.S. climates, the energy savings over the lifetime of the window are likely to be less than the cost to replace the window. Many studies have shown payback periods of 60 to 100 years for windows -- and replacement windows may not last that long.
There are many variables, of course. The colder the climate, the greater the savings. The better the window glazing, the greater the savings (but note that the investment is also higher.) Energy cost inflation assumptions vary from expert to expert. Nevertheless, it's very hard to make window replacement pencil out, from energy savings alone.
Still, people replace windows all the time -- often for comfort reasons, or for ease of operation. But if you are after energy savings, just buy some good low-e storm windows.
Upsizing the burner just one size is one thing...
But more often than not existing stock is 2, 3 even 4x oversized for the design condition load, if the ducts are reasonably designed and sealed. The standby & cycling losses of a low-mass hot-air furnace are low, but non-zero. At 3x oversizing an 80% gas furnace will do no better than the low 70s for AFUE (according to DOE curves established by the LBNL see: http://www.osti.gov/bridge/servlets/purl/6519-OB2P9G/webviewable/6519.pdf.) But for multi-stage condensing units that pretty much goes away- even if the high-fire is 3-4-5x oversized at design condition, it's the low-fire output that determines the end point of the curve.
But for non-modulating high-mass cast iron hydronic boilers the cost of oversizing is more severe, and needs much closer scrutiny. If the boiler is fully within conditioned space the standby loss accrues to the conditioned space, but there are still cycling losses. Strategies for mitigating the efficiency hit from very-oversized boilers vary, but heat-purging economizer controls (there are a handful out there) that "learn" to anticipate when the thermostat will be satisfied and cut the burner ahead of time, purging the residual heat in the boiler into the zone, and delaying the start of a burn on the subsequent call for heat until the boiler reaches the programmed minimum tend to save double-digit percentages on fuel use. This works because the boiler & distribution plumbing are always parked at a lower temp at the end of a burn for lower standby loss, and the average temps are cut significantly. For non-condensing boilers this is usually a more effective approach than outdoor reset (ODR) control, as it maximizes the burn lengths utilizing the thermal mass of the boiler with a high hysteresis, whereas ODR results in a far greater number of lossy ignition cycles at the low end of operating temp.
Standard Manual-J & similar methods of heat loss estimating are by nature oversizing, and also subject to garbage-in-garbage-out errors (usually to the high side) by the contractor who never want's to get the 5AM call on the coldest night of the year from an irate and cold customer. Oversizing is endemic, and easy to do- when the heat loss calc overshoots by 25% when done perfectly, and with contractor data entry bias bumps it another 25%, then they upsize it another 25% percent because that's the first size bigger than the calculation called for you're already at 2x oversizing (1.25 x 1.25 x 1.25=1.95). AFUE tests assume duty cycles at 1.6x oversizing, not more- if one selects the even next size up in the boiler or furnace size "just to be sure", it's usually a significant enough step that you'd be bumping on if not exceeding 3x, and on the steeping part of the curve for even a low mass hot air furnace. (And this is COMMON.)
For an existing installation it's easy to put an upper bound at design-temperature heat load by doing the simple arithmetic on fuel use at the equipment's steady-state efficiency ratings against heating degree-day weather data. eg. If in one year the house uses 800 therms of gas over a 4000 heating degree days (HDD, base 65F outdoor temp) heating season that is 20,000BTU per degree day. In an 80% furnace that's 16000 BTU per HDD. Dividing by 24 you get 667BTU per heating degree. If the 99th percentile outdoor heating design temp is 15F, that's (65-15=) 50 heating degrees at design condition, and the heat load is 667BTU x 50= 33,350BTU/hr.
That's a very realistic scenario where a 100K+ furnace or boiler might be the heating appliance. This situation is common, and guaranteed to be 3x oversized, possibly 4x oversized depending on the particulars of where the mechanical room's location & insulation is, and something to take into consideration when updating the equipment. No matter how tidy, clean & official the contractor's heat loss calc printout might look (if they provide one at all), it doesn't trump measured reality.
If heating hot water with the same fuel, knock off 150-200therms from the annual fuel use number for a better guesstimate (more if it's a 5 person shower-hog family.)
Lidded pots
I've put some thought and experimentation into energy efficient cooking and I'm convinced I could prove that lidded pots do save energy. Say you want to make mashed potatoes, and have a pot with potatoes and water. The idea is to simmer until the potatoes are tender, maybe 20 minutes. What a lid does is to allow a lower heat setting to maintain simmering temperature in the pot. It's pretty clear to see--leave the lid off, and the water goes still. In fact using lids requires more attention from the cook because holding in the heat and steam can cause pots to boil over. To avoid boiling over, you turn the heat down.
Windows
I understand every point that Martin is making about windows- I have heard it many times- but there are a few points that engineers never (rarely) take into account in the window replacement argument. (And I get that this is the engineer's job- cold hard data- and 'get a storm window' is the answer when you are just looking at the cold hard data of energy saving vs cost of new windows - both monetarily and in embodied energy. So fine- I get it.)
BUT, I am an architect and I am very pro 'window replacement' for the following reasons:
1. Good windows DO save energy and money. (Ok you don't get to full payback on energy alone.)
2. Good windows give you the actual feeling of comfort in a house- better than a storm does (believe me I live with both right this second.) You do not have the experience of sitting next to a very cold surface with a good new window.
3. Safety. Most old windows barely open. Add a stiff, hard to operate storm window (and we all know they are that way) and you double the problem. I changed the windows in the house I live in when my 7 year old was afraid of fire and kept asking me 'but how mommy- how can we open the windows and get out?' I looked at our crappy single pane double-hungs with their impossible storms (that, btw, no fireman could fit thru), and I put an ax next to the window in his bedroom and ordered new windows. Neither me, my son or my 72 year old mother could open any windows in the house more than a crack when the storms are on in the winter. We don't have the strength. There are THOUSANDS of houses like this in the U.S.
4. Aesthetics. Want to up the value of your house? Want to get some curb appeal? Try new windows. Yes some historic homes look way better with their original windows but most houses built between 1940 and 1990 would be greatly enhanced with decent windows. This may seem like a minor point to some but - hey - your house is your biggest investment. Re-sale is usually important. Windows often 'make' the house.
5. Leakage; Leakage DOES matter. Even if it is not as much as your attic or basement (Note also that one of the things on the recommendation list (above) is to have a blower door test and another is to insulate the attic ONLY AFTER sealing the ceiling below the attic - so it MUST matter right?) When you replace your windows you actually have a chance to do it right, kill much of the air infiltration and also stave off, or mitigate a lot of moisture rot. We all know that basically every house from the 50's and 60's with single pane windows is rotting at the sills as we speak - if they have not already been cobbled with trim, flashing and caulk 'band-aids' many times already.
Anyway- I know the point Martin is making about windows is valid- sort of- but I am so tired of the green industry telling everyone to not waste their money on new windows!! These 5 other reasons are very strong reasons to get new windows and I think we should all be taking a more integrated, whole house approach to our buildings. And speaking more carefully about getting new windows.
Also - curtains in the windows may not really help- by the numbers- for keeping your house warmer/ saving energy- BUT they sure do make you feel better in a room with those cold windows in the winter....
Elizabeth
Response to Elizabeth DiSalvo
Elizabeth,
I think we agree. There are many reasons to replace windows, and you have listed some good ones. Anyone who finds your reasons compelling, and has money in their pocket, should replace their windows.
And we both agree that it doesn't make sense to replace your windows if you're doing it to save money on your energy bills. For someone in the latter category, there are half a dozen measures that make much more sense.
Myths about windows
I understand the general problem - that is window replacement is expensive. But at times it seems like the optimum path. I am considering getting some of the R5 windows from the DOE High Performance Windows Program (R5). My windows are very leaky, single pane, wooden, that open out in the middle and leak like a sieve. I don't think storm windows over this combination will be very effective.
It is more important to me to save the energy then to save the dollars. Obviously window replacements are labor intensive so much of the cost is not in the embodied energy of the window.
After air sealing, insulating the attic, changing the furnace, hot water heater, and frig. sealing the crawl space and insulation crawl space walls, the next steps seem to be thickening the envelope or changing the windows. Am I missing something fundamental? Again the object is to save energy rather than save money so the payback is not high on the consideration list.
Outlets
Regarding outlets, I can't speak to the volume of air, but there is no question that on windy days in my 1931 house before we put cellulose in the walls, I could feel jets of cold air coming out of the outlets. And the foam plate thingies didn't help; it came out of the outlet sockets themselves. I put in child-proof caps to plug them a bit.
After retrofitting insulation it's much better, air doesn't flow so freely...
Response to Pat Murphy
Pat,
You wrote, "It is more important to me to save the energy then to save the dollars." Obviously, if your goal is to save energy without regard to cost, then cost-effectiveness doesn't matter.
It's possible that Jesse Thompson would argue that installing a PV array is (at least in areas of the country with high electrictiy costs) a better investment than window replacement.
Response to Eric Sandeen
Eric,
You write that before you insulated your house, you could feel air leaks through the electrical boxes on windy days. So I agree -- it's a good thing you installed cellulose insulation. I hope that your insulation installer also plugged air leaks in your ceiling.
One thing I can guarantee you: if you could feel air coming through your electrical boxes, you had some enormous holes in your ceiling. I hope those holes are plugged now.
windows...
I should clarify -- I have nothing against people getting new windows. There are many reasons to replace your windows just like there are many reasons for doing a wide range of home improvements. it's just that windows typically pay for themselves in energy savings only slightly faster than granite counters pay for themselves in energy savings ;)
For comments that have wondering if my conclusions were based on ignoring air leakage or making bad assumptions about solar gain or other things like that,, the bottom line is that my conclusions are based on actual energy savings from analysis of utility bills that also match up quite well with engineering calculations. It's when you make a calculation and then find data that agrees with it that you start to think you may have something worth sharing with others.
Measured savings from window replacement have been assessed in multiple billing data analysis studies done in Oregon. People in Oregon who got a rebate for having installed new Energy Star windows showed a reduction in their gas bills that averaged about 0.2 therms/yr per square foot of window -- or about 40-50 therms/yr for a whole house window replacement job (200-250 sq.ft.). Since a therm of gas only costs about $1 now, that's annual savings of maybe $50/yr .Given the typical cost to replace all of the windows in a house, the payback period is likely to be longer than 100 years. In a colder climate, the savings should scale with degree days, although i found savings of about the same magnitude looking at a small sample of homes in upstate NY that replaced their windows.
The savings of $50/yr are just an average and so some houses will save a good deal more than that. If you are starting with just single pane windows and no storms, you might save 2 or 3 times as much as this average value. If you've got all jalousie windows then you might save 5 times as much -- they hardly even close. But most homes in cold climates have two layers such a wood single prime plus an aluminum storm window and the payback for replacing these is not so great -- even when they are not in great shape.
So, the bottom line is that if you want new windows, then you should get new windows, just don't expect them to pay for themselves with energy savings any time soon.
Furnace over-sizing
My conclusions about furnace oversizing were in the context of installing a new 90+% furnace -- not installing a 40 year old atmospheric furnace or high mass boiler. Dana Dorsett pointed to a report which is one of the references I use to show how oversizing modern furnaces does NOT have a big energy penalty. That report shows that modern sealed combustion furnaces have low cycling losses -- in fact the report says
" All this implies that sealed combustion systems that are isolated from the building should have little to no part load degradation, since they eliminate the stack and flue losses. There may even be a slight increase in efficiency as part load, as shown in Figure 6"
The issue is whether there are any significant energy savings from picking a slightly smaller furnace because you did a Manual J calc compared to ending up a size larger than that. I haven't seen any good data that shows energy savings from this. I'm not in favor of oversizing systems-- but the main reasons for proper sizing are about ductwork, noise, and comfort more than about energy savings. When it comes to over-sizing by just one step, even these reasons are often not that strong.
Lidded pots
TJ Elder -- you are correct. there is no question that when you put a lid on a pot the water will boil faster or the contents of the pot can be kept hot at a lower burner level. The issue with this tip isn't whether it works as expected, it's how much energy that adds up to over the course of a year. For most people, it's just not a whole lot of energy.
I certainly wouldn't want to discourage this behavior -- I cook with lids all the time -- I just wouldn't want someone to pick this as one of the 50 simple things they do to save the planet while they keep their second fridge plugged in in the basement.
Eric S
Martin -
Yes, we insulated and sealed the attic too... I've had a blower door / IR test as well, and it came in at 1400CFM at 50 pascals ... That's actually fairly low for this old house if I'm not mistaken.
IIRC the "windy outlet" problem (and the blower door) was after an initial stab at attic sealing, but they missed a laundry chute that was open to the attic. (sigh.) Insulation and another go at the attic came after that. Suppose I should re-do the blower test.
Anyway, doesn't make it not a myth I suppose; in any reasonably tight house it seems unlikely that the outlets are a significant issue.
I'll add "unplug your cell phone charger" to the list of myths, unless your charger was made a decade ago. My iphone charger doesn't register even 0.01 amps on my kill-a-watt. Vampire loads are real, but you'd do well to measure to find the ones that actually matter.
Response to Eric Sandeen
Eric,
My point was that if you can feel air coming in around your outlets, it's a good bet that you have huge leaks in your ceiling/attic floor. Your report confirms that my guess was accurate. Fixing the attic leaks usually solves the leaky electrical box problem.
I agree with you about phone chargers. They are a very minor issue indeed.
windows SIR
The only reason windows don't have a healthy savings to investment ratio is because of the labor costs involved in installation. If you can find a sweatshop of highly skilled window installers, working for below minimum wage, then you're golden.
I think Martin needed a more controversial topic
OK, since no one else has taken exception to the lead in, where it is advocated that cleaning the condenser of a refrigerator is no longer needed (it is implied, although I do acknowledge that Martin prefaced it with "for energy efficiency reasons"). There are other reasons for performing maintenance; cars still need their oil to be changed, although I believe the mileage improvements (i.e., improvement in energy efficiency) can be demonstrated to be minimal, at best.
I also take exception to the quality of the stud(ies) referenced as "proof". Be careful, there are lies, damn lies and statistics; the studies referenced from the energy magazine were, to use the phrase... poor. They were hardly controlled experiments. And unless the laws of thermodynamics have been changed since college, I believe you still need a certain amount of energy to be transferred to the environment for the refrigeration cycle to work! I would agree that the refrigerator designers probably oversized the surface area of their condensers to permit operation of the refrigerator, even when caked with crud, although I still wouldn't, knowingly, let the refrigerator run for long periods (especially in the summer!) with all that junk on the condenser...even if the brush cost more than I would save in electricity....
Finally, since we're now advocating running refrigerators at their design limits, how much money/energy does it save when we have to replace the refrigerator because we didn't maintain it....
I still think Martin wanted a more lively topic this week....
Lights
Electrical openings also includes ceiling light fixtures, smoke and CO detectors. These contribute to stack effect leakage and are part of the 7 t0 10 cfm50 per electrical opening estimate. Mechanical openings in exterior walls must be of some importance if Passive House goes to the trouble of adding an airtight OSB layer and then straps a separate wiring chase.
Where's Psychology Today when you need it?
Our insistence on believing these myths about (energy savings) is a fascinating topic in itself. I'm a mechanical engineer- I've run the numbers, I've read the reports. I "know" the payout for windows is longer than my expected lifetime (and not just because I'm old.) I'm looking at buying a house w/ 35 single pane windows, about 3'X6' and I feel in my heart of hearts that the first thing I gotta do is replace all those windows w/ some modern ones.
The house hasn't been updated since it was built in the 50s, so sealing all the holes in the ceiling and floor, insulating the walls, putting more than 3-1/2" of insulation in the attic and adding a programmable thermostat are my most cost effective choices, by a factor of at least 20. But no, my mind keeps going back to those damn windows.
Dust on refrigerator coils is probably about R0.3, but by golly, when you've dusted them, you can SEE the difference and if you can see the difference, it must be real.
Maybe it's that I'll be able to see the windows- I can't see a leak into the attic and I won't be able to see the foam that will plug it. Likewise more insulation- even though I blew 12" of cellulose into my current attic and immediately noticed the house was cooler in the summer. The insulation is out of sight, and so, maybe out of mind? I can FEEL cold air coming out of my outlets, so it must be real and significant. I can't feel warm air rushing up into my attic, so it may be just a figment of Martin's imagination.
Humans just aren't very good at dealing with abstract concepts like R values and delta Ts, partly by nature and partly because we're poorly educated. All those ads in the newspaper touting energy saving windows don't help either. Columns like this one are important, but face it, all us folks reading and commenting are nerds. Not even Public Broadcasting runs programs on "Understanding SHGC in Mixed Climates." Holladay and Blasnik have never been on "Meet the Press. Lstiburek is just not a household name.
another reason for putting lids on pots
If you cook much at all, the water content you add to the air in your house will be significant if pots are not lidded. In a relatively tight, insulated house (or one with leaks in the wrong places) that is not fitted with the proper equipment for handling this, you could get into a lot of trouble.
I would skip the lidded pots myth next time around. The point is not that it saves energy but that it controls humidity and pots come to a boil faster. There is no effort in doing it. The energy savings may be trivial, but it's also trivial to call it a myth.
On windows, refrigerator coils, and cooking pot lids
I think Robert Fankhauser's comments are the most perceptive -- thanks. You're right: most of the things that energy experts advise people to do are invisible, and no one wants to spend $1,000 on something that is invisible. We find it hard to believe in the effectiveness of an invisible measure.
To all of you who have written comments noting that there are many good reasons to replace windows, clean coils, and put lids on your pots: sorry, but you all missed the point. Michael has no problem with anyone who wants to replace their windows, clean their coils, or cook with pot lids. Neither do I.
For the record, I have spent thousands of dollars I can barely afford to put triple-glazed windows in my living room, and I will never see energy savings to justify the investment. My refrigerator coils are clean. And I always cook with lids on my pots, unless I am doing a sauce reduction.
There are many reasons to do all of these things, as GBA readers have pointed out. But saving energy isn't one of them.
We've all seen the lists. In the 1970s, they were headlined, "Ten Easy Ways to Save Energy In Your Home." These days, the headline usually reads, "Ten Easy Things You Can Do to Save the Planet." What drives me crazy -- and what probably drives Michael crazy -- is that these lists often include items like "replace your windows," "clean your refrigerator coils," and "cook with lids on your pots." But when researchers do the math and measure the energy savings, they tell us, "Those items don't belong on the list."
So go ahead and do them if you want. Just understand why you are doing them.
Re Martin
.
Apologies, but my typing skills are lacking and I took this out to wordpad to edit, hope it is at least minimally readable
>>>>>>>>>>>>
1. First of all, your estimate of the market penetration of high-efficiency furnaces (with efficiencies over 90% AFUE) is much too low. In some markets like Wisconsin, 85% of all residential furnaces sold are high-efficiency units. While the market penetration in other areas of the country is lower, most cold-climate regions have moved to high-efficiency furnaces.
>>>>>>>>>>>
They may be condensing, but unless they are variable firing rate, they will use more fuel to run if they are oversize. Most are not variable rate. Added to the higher cost of the unit, as larger units are more expensive. So they do waste energy, the magnitude of that waste is subject to debate, but it is there, and it cost you more to oversize, so why are you doing it? And why are you defending it?
>>>>>>>>>>>>>
3. Neither Michael Blasnik nor I every said that "Windows don't save money." Obviously, the replacement of old single-glazed windows with new double-glazed units save energy. The question is, is the investment cost-effective? The answer is no.
>>>>>>>>>>>>>>>>>>>
First, in Michael's post he compares the cost of windows to the current cost of natural gas. . Hell, if the head of the natural gas council said 'don't insulate, buy my cheap gas' you would have his head on a pike marching down main st. No one in their right mind thinks that the supply demand curve for natural gas will stay the way it is now.
I cannot get natural gas, and oil is 3.80 per gallon. 3 1/2 times the cost of gas. Kinda changes the math. Over 30 percent of us in the northeast use oil, a significant fraction because there is no gas in the street.
>>>>>>>>>>>>>
5. It is undeniable that when you replace an existing single-glazed window with a new double-glazed window, the new window will have a lower SHGC than the old window.
>>>>>>>>>>>>>>
Of course, but it is not zero, you of course are not arguing that lo e windows eliminate solar gain
>>>>>>>>>>
6. It is extremely rare to have a house in which all windows were so shaded that SHGC was irrelevant. Perhaps if every single side of a single-story house had deep porches, your scenario might occur. That almost never happens
>>>>>>>>>
Most existing houses are not sited for solar gain. 3/4 or more of the windows are solar irrelevant. As I type I am about to put a hat on, because at 7:30 AM the sun is going to be in my eyes in a few minutes, but in 3 hours it will be partially obscured by 40 foot pines, and will remain so for the rest of the day. I have the best solar siting on my street. Yes, I get great morning solar gain, but only a fraction of what the charts would tell you was possible[or what I would get had I built the house] I feel this is quite a normal situation. half the houses on any given street will have less than prime solar siting at best
>>>>>>>>>>>>>
7. Your statement, "in a normal house half the heat goes out the windows," is meaningless. What's a normal house? In any case, even in a house in which half the heat loss is attributable to the windows, window replacement isn't cost-effective.
>>>>>>>>>>
I'm sorry but is is no more meaningless than blanket statements like windows don't pay
1000 square foot house, on piers, ignoring leakage:
1000 square foot roof R40
1000 sq ft walls R20
200 sq ft windows R2
1000 sq ft ft floor R40
I am ignoring leakage to simplify, assuming the will be no change from changing the windows
Delta T 50 Degrees
heatloss roof 1250 btu
floor 1250 btu
walls 2500btu
windows 5000btu
funny how that works
If that house used 500 gallons of heating oil for the season, a rational number, and you doubled the r value of the windows, you could assume that the savings would be 25 percent, amounting to 475 bucks at 3.80 per gallon. You recently listed Intus windows at shy of $40 a square foot, which should perform better than my R 4 assumption. The windows are paid back in 16 years, the labor may take another 16. But of course, your assumptions were for 'zero' cost for your existing windows, which is probably not valid. There are bound to be cost associated with repairing old wooden frames, and replacing failed igu's
Solar gain on the E, W and N sides may be measureable, but is so low as it should not be a deciding design factor. Even if the house had a true south facing side, in my area the number in my head from years back was something like 64 btu sq/ft max hits south facing glass. SHG number for double pane clear is about .7, high gain lo E about .5, you would be getting 32 instead of 45. assuming the windows are clean.......
Here is, in my opinion a true statement:
If you have access to cheap heating energy, and think it will stay that way, and allow the guy with the bad sport jacket and greasy hair to gaff you to change the existing thermopane windows out of your 1990 house for some supposedly lo E vinylly replacement things you will never see payback.
And another thing......
I can tell Martin must be sneering as he types 'comfort'[and goes out to split some more wood] but it is actually an interesting issue.
Why don't 'bad' houses use as much heating energy as they should?
One reason is that when the thermostat, sited in the middle of the building, ceases calling for heat at 68 degrees, half the house is not 68 degrees.
So, one way to think about it is that a well insulated house's heating system does more of its job than a poorly insulated one does. With the same thermostat setting a well insulated house is kept warmer than a poorly insulated one, and is more 'comfortable'
So if we turned down our thermostats to represent the true average temp after improvements it would be a truer measure of savings.
Let me know if you think of a way to sell that one to my wife.
Keith- where do you live?
I'm just wondering where a normal house has R-40 attics and floors and R-20 walls but just R-2 windows? I don't think I've ever seen such a house. You could have also tried to support your point about half the heat leaving through the windows if you picked a greenhouse as your example, but that wouldn't be much more normal than your example home.
But more seriously, you are right that if you have oil heat the payback for windows will be much faster than gas heat at $1/therm. Let's see, at $3.80/gallon the average annual savings (translating 0.2 th/sqft/yr) would be about $7 per year per window. So now you might be looking at a payback of under 100 years -- they might even pay for themselves before they are replaced again, but probably not.
Back to your furnace argument, you seem to have missed the point that the modern sealed combustion furnaces have very low cycling losses and therefore picking a somewhat larger unit has very little if any energy penalty -- there is no need for this to be a multi-stage unit. Please cite any study you can find showing the energy savings from downsizing modern furnaces. I'm not in favor of oversizing systems but I'm also not in favor of misleading people about the energy savings.
Sneering?
Keith,
You wrote, “I can tell Martin must be sneering as he types 'comfort.'”
I'm sorry, Keith, but your sneer-o-meter is faulty. I sneer not. Anyone who has read my advice over the years know that I have always advocated in favor of the installation of triple-glazed windows in cold-climate homes, citing the improved comfort that such windows provide.
Cost efficiency
Cost efficiency is one of the hardest things to argue because it is so difficult to predict the future:
As long as the government still give incentives to oil and gas companies and other energy providers we don`t know the true costs of energy. We know that Americans use twice as much energy in average than Europeans and 5 times as much as the worlds average (http://www.novatlantis.ch/en/2000-watt-society.html). Maybe because in this economy things that make sense are not cost efficient. Maybe we should change the way of thinking and stop buying crap so we can afford some of these "non-cost effective" things!
Things that are also not cost efficient:
- working in the building industry
- buying food from a co -op
- driving (incl. buying) a fuel efficient, hybrid or electric car
- spending time on the GBA website
.....
Extrapolating Hidden Truths in Some Myths
Since I own and manage 25 rental houses, I have some anecdotal comments:
1. Furnaces are very reliable and clean filters don't save energy. True. However, a missing or ill-fitting filter will shorten the life of the blower motor. Fuzz and lint will build up on the motor, which insulates it, causing overheat which can cause it to "burn out".
2. I suggest that the "window replacement" number crunching be redone using $179/window AND the assumption that each new window adds $140 to the resale value of the home. Most cities have a company advertising this price.
3. Refrigerators with linty coils are OK. However, I've had fridges and wine coolers built into tight, unvented alcoves or cabinets. In this case, they just DON'T WORK.
4. Ceiling fans in winter (even blowing upward) get the air moving. Moving air below about 90-100F usually feels cooler than still air.
Response to Philipp Gross
Philipp Gross,
Fair enough. But if an energy expert can show us that it makes a lot of sense to perform blower-door-directed air sealing, to insulate our walls, to insulate our attics, and to replace our old appliances with new efficient appliances -- but that it makes much less sense to replace our windows -- that is very valuable information, because it can inform homeowners where to start. First things first.
re: Martin
What fun is left around here if not to poke fun at your relatively spartan existence
Re Micheal
The point would be that if I had used an example with less than code insulation, then I would have seen noise about the relative value of insulating. And they would be right.
R2 is a standard clear double pane. The skinny 3/16 spacer windows that came on my house run about R1.8 as I see quoted. They were installed in the last 12 years sometime. Your Energy star windows are mere r3 as of 2010
My example is a pretty normal small house built whenever they upped the walls to R19[forgive my roundy numbers]
It is no closer to a greenhouse than a house in Portland[do they even close the windows there?] with Energy Star windows[ worst case, lo solar gain, marginal R value] defines that windows do not ever pay back, no way, no where, no how.
Oh, and how about...
Standard circa 1970
R11 wall
r30 roof floor
r1 windows
4545 walls
3333 floor/roof
10000 windows
and that is a common house around here
Keith's 32-year payback for windows
Keith,
I'll let Michael continue to argue with you on the math. He's doing a good job.
But just for the sake of discussion, I'll accept your numbers. You explain that the payback for window installation is 32 years. So a homeowner who is 50 years old will break even when they are 82 (again, using your assumptions) -- assuming they aren't in a nursing home at that point.
Anyone who wants the comfort of good windows should go ahead and replace their windows with new ones. But if they want a faster payback than 32 years, they should think first about air sealing, insulating, and replacing their oldest appliances with new, more efficient models. That's all Michael is saying.
windows
What Martin said....
The bottom line is that window replacement is generally not a big energy saver and many energy savings claims are overstated. We need to be honest about the energy impacts of different retrofit strategies -- it doesn't help anyone but shady contractors to make bogus claims.
I am looking for Keith's study showing 25% heating savings from window replacement measured in a large group of homes. Maybe that study was done in the same land where 1970 homes were built with R30 floor insulation, R-30 attic insulation, R-11 wall insulation and R-1 windows. In my experience, the vast majority of homes in heating climates with R-30 attics have double pane windows or single plus storm.
Also, as an interesting aside, there really aren't R-1 windows -- even single pane windows are likely closer to R-1.3 or 1.4 in real world performance because the interior and exterior surface film heat transfer rates are lower than the standard assumptions that have been commonly used. This over-estimation of surface heat transfer is one of the many reasons that energy simulation models tend to systematically over-estimate the energy use of low efficiency homes.
Kevin -- $179 windows?
What kind of window can you get for $179 each installed? What kind of performance / specs? Will those windows really boost the value of your home by $140 each? Will they still be boosting the value of your home in 10 years?
Of course, if you want to count the increased resale value from the windows, then you can't count the energy savings that occur after you sell your home either (you've basically sold those savings to the next people) -- so you need to sell your home fairly quickly to get that large resale value but then you don't have many years of energy savings for the payback. It might work out if you get a really good deal on the windows and high resale value. But windows are still not likely to make the priority list for making your home more efficient.
re
"The bottom line is that window replacement is generally not a big energy saver and many energy savings claims are overstated."
Now that is a true statement
It is quite a different statement than window replacements 'never' payback.
Um, my house, when built [in 1970] had R11 in the walls[R7 in one bath] R9 in the roof and no foundation insulation. There are at least 2 other similar [glassy] houses in my immediate neighborhood with single pane glass.They all have on the order of 750 square feet of glass, single pane.
Thermopane windows did not become fashionable until after the 1973 oil shock. My next door neighbors house of similar vintage has single pane glass except for patio doors that have been replaced.
IIRC the r value of a pane of glass is in fact, nearly zero, on par with concrete at .08 per inch. It is the air layers that give it any value at all.
Look, I get it, windows are a profit center for large corporations, and really cheap air sealing and insulation measures are much more cost effective. But once you do that[as in my first example] windows are where it is at.
I can just picture the guy sitting in his living room, stoking up his coal fired boiler as the breeze blows through his 1866 windows , "Nope Martin and Michael told me not to replace my windows, not cost effective"
I stand by my scenarios, as limited as they are. They are in no way out of the ordinary buildings in Eastern Mass. I think your quoted study is biased[not by intent I am sure] because of the relatively mild climate in Oregon and the comparisons of very cheap energy.
And again, you are comparing[new replacement windows] to Zero, which is profoundly unrealistic
Response to Keith
Keith,
I can assure you that the many window-replacement studies out there are realistic. You wrote, "You are comparing [new replacement windows] to Zero, which is profoundly unrealistic." I have no idea what you mean.
re Martin
Zero as in zero cost for the existing windows. There are no forever windows, and IGU's made in the 70's thru 80's don't last nearly as long as later ones due to better sealing technology. Wooden frames made of the infamous broscowood start rotting as soon as the contractor backed out of the driveway.
$179 Windows vs. Storm Windows
Michael,
They are just medium quality vinyl, double pane. The upcharge is $30/window for low e.
My main point is that they are vastly superior to storm windows and probably don't cost more.
Completely neglecting energy savings (which could be close to a wash) I would counsel everyone in a non-historic house to go with new windows vs. storms. Less future maintenance , and better resale value.
Electrical openings, The 1 percenters
I will try to explain a bit about air leakage at electrical openings and their share towards overall building air leakage. Martin used a figure of 1% of the total and claimed most electrical openings are in the neutral pressure pane and are not a factor unless the wind blows. I made the statement that a good energy rater said a typical electrical opening in an outside wall will show a leakage rate of 7 to cfm50.
I do not use 7 to 10 cfm50 and believe about 1/2 that amount is closer to reality, I have come across pie charts over the years showing the share of infiltration for electrical openings at 1 to 2% for standard built homes. I will use the 2% for now and would welcome feedback from anyone who can put a more definitive percentage on it.
EqLA
http://www.buildingscience.com/glossary/equivalentleakage
When I broke into the superinsulation game in 1983, double walls, tri-pane windows and low ach50 were the rage, they still are if you are looking for maximum efficiency. The Canadian R-2000 program set as a maximum infiltration target, 1.5ach50, a worthy minimum standard still today. Homes I built in that era tested around 1.25 ach50 that sometimes included rooms over garages (tough on surface to volume ratio). The person performing the blower door test would also express the air leakage for the building in square inches ( EqLA). If I recall correctly the EqLa for these homes was around 50 to 60 square inches about a 7" x 8" hole, this is for the entire building envelope.
Back to the 1 or 2% contribution of electrical openings to the overall infiltration for the building. This figure is most likely correct for homes built and referenced in the pie charts of the day. These same homes probably had an ach50m of near 10 so the electrical openings were indeed a small part of the total.
I disagree with the assertion (most electrical openings are located near the neutral pressure plane). They are in fact quite uniformly located throughout the walls and ceilings, especially in a 2 story house.
In modern energy efficient housing, electrical openings if left unattended, can contribute far more than 1 or 2% to the overall air leakage, here's why. Let's say the typical home has 40 electrical openings and each electrical box has 2 knockouts removed (about 1/2 square inch) We are now looking at an EqLA for the electrical openings of about 20 square inches, less the space taken up by wires. My 2 story homes had a total EqLA of 60 inches, this 20 inches would 1/3 of the total leakage area. Older housing with ach50 rates 10 times higher would have a similarly higher EqLA so the percentage of air leakage for electrical openings as a percentage of the total would be far lower.
The moral of the story is, percentages can be misleading, dig into the numbers. If your goal is to build energy efficient homes, all leakage areas must be addressed. When you put the total leakage area (EqLA) into the mix, you begin to realize just how tight a tight house is and how detailed the air sealing must be.
I have the highest respect for Martin but like to challenge him from time to time, his contribution here is invaluable to those looking to build better.
Response to Doug McEvers
Doug,
1. You wrote, "Martin used a figure of 1% of the total."
Actually, no. The people who used a figure of 1% of the total were Rick Diamond and Mithra Moezzi, not Martin. Martin was quoting their paper; the link was provided. Diamond and Moezzi cited ASHRAE Fundamentals 1997 as their source.
2. You wrote, "...and claimed most electrical openings are in the neutral pressure plane and are not a factor unless the wind blows."
Actually, no. Diamond and Moezzi are talking about "electrical outlets" -- that is, wall receptables -- not electrical openings. I have always been a strong advocate of sealing electrical penetrations in ceilings and electrical penetrations between a basement and the first floor, as even a cursory review of my air barrier articles reveals.
3. You wrote, "I disagree with the assertion (most electrical openings are located near the neutral pressure plane)."
Once again, Doug, you are confusing Diamond and Moezzi 's discussion of wall receptacles with "electrical openings."
Response to Kevin Dickson
Kevin,
If you pay $179 (materials and labor) for the installation of a "medium-quality vinyl window," how much do you pay for the installation of a low-quality vinyl window? And what features does your medium-quality vinyl window have to distinguish it from a (presumably even cheaper) low-quality vinyl window?
After all, it can't be "medium-quality" unless there are cheaper windows available.
Second refrigerators/freezers
One of the energy tips -- one I'm surprised nobody has commented on -- is to "unplug second refrigerators and freezers".
In my case, unplugging the second freezer would cost several hundred dollars' worth of frozen food. That'd be why I have a second freezer -- to keep things frozen. Unplugging doesn't sound like a good plan, as the freezer doesn't work so well when unplugged.
In fact, anyone unplugging a second refrigerator or freezer would, it seems, do better to get rid of it. Storage cabinets (recycled from that kitchen remodel you KNOW you're dying to do) can hold more stuff in less space, and the refrigerant in the old refrigerator can be recycled instead of slowly leaking out over the years.
Would not a better tip be, "Assess your need for your second refrigerator or freezer, and eliminate it if not needed"? Pair that with, "Do not put a second refrigerator or freezer in a hot place, like a garage, where it will have to work twice as hard to keep cool."
Some commentary about the cost-effectiveness of replacing an old refrigerator with a modern Energy Star appliance, and comparing a chest freezer to an upright, could also be useful.
[Editor's note: Click page 2 to continue reading comments.]
Response to Darrin Brightman
Darrin,
You have correctly interpreted Michael Blasnik's point, I'm happy to say. Like you, Michael does not advocate letting food spoil. So by all means, eat the contents of your freezer or second refrigerator before you pull the plug.
All too often, as I'm sure you know, one member of the the household decides that it's time for a new refrigerator. Once the new refrigerator is installed, another member of the family decides that the old refrigerator should be dedicated to beer. This second refrigerator is usually unnecessary and always contributes to high energy bills.
Close your curtains on winter nights. (This advice only makes se
'Close your curtains on winter nights. (This advice only makes sense if your curtains include a mechanism to seal the perimeter of the curtains, including the top, to prevent convection currents).'
Firstly, this qualification should also include sealing the bottom of the curtains, as most curtain fabricators in our locality make 'to the floor' the curtains hang 5mm off the floor. Without the bottom sealed the curtains are like a bucket with a hole in it.
Obviously sealing the perimeter will improve the efficiency of the window, however to say that closing curtains in winter is ineffective, is I believe incorrect. As heavy drapes + pelmets have a resistance to heat of 0.330m2.k/w they have a resistance to heat flow out even if there are some convection currents reducing there potential effectiveness.
Personal experience has shown noticeable reduction in energy use in winter when we installed curtains(without pelmets or sealed perimeter) and a thermal imaging camera clearly shows the effects of a closed curtain both in summer and winter(and yes I know that it is more effective to shade a window externally rather than internally in summer).
To put it another way convection is not the only way to lose or gain heat.
Response to Chris Lockhart Smith
Chis,
I agree that the word "perimeter" includes the bottom of the curtain.
Refrigerator coils: not cleaning them a slight caution
If studies show that cleaning the coils is not necessary that is fine. Cleaning the coils and general area (under the refrigerator) does help to prevent at least one problem. Whne fan is off, if a glob of accumulated lint falls on the fan blade , it can stop the fan from turning/starting when the refrigerator "kicks" in. Sounds odd? It happened to my refrigerator's fan. The quiet running fan is apparently also not overly strong. Clearning also helps remind me to routinely clean the condensate drain tube :}.
Studies
There seems to be a lot of hand waving in these threads, and a lot of 'absolutes' being specified. (Like, it replacing windows is not cost effective, etc.) How about specifying how to calculate how to make the cost/benefit analysis rather than just stating doing various items are or are not 'cost effective'.
Yes, this is the old engineer in me showing up... I guess I was a geek before being geek was cool.
... On the cleaning the fridge coils, well it can't hurt. Try putting a kill-a-watt or similar unit on your appliance for a few days before cleaning and after. Check the difference to see if the power savings is what someone might consider 'cost effective'. It would be one data point, and not enough to extrapolate to a generality, but reporting data points (with information about model, age of unit, etc) could allow collecting enough data so it could turn into usable information over time.
Just some thoughts from an old geek.
comment on lighting efficiency and some other thoughts
Had to add a comment on CFL's vs. incandescent bulbs. When you are heating a home, the heat given from a incandescent bulb helps reduce the heating load. Conversely, the very inefficient incandescent bulb puts an additional load on air-conditioning. My understanding is CFL's have traces of mercury and I know they are difficult to recycle. But if I lived in a cool climate with many months of heating - I would not be too worried about improving the lighting efficiency inside my home. Of course, outdoor lighting like street lamps, should utilize the highest efficiency lighting technology like LED. Never-the-less, the electrical loads found in a home - even a personal computer - ultimately convert their electrical energy input into heat and they do that at 100% efficiency. Therefore, I don't see how you can claim ALL of the energy savings when converting to CFL or LED lighting.
When measuring efficiency - I've always felt that it is important WHERE you establish the system boundary .
Opening WIndows in Winter
As an American now spending time in Austria I find that one area the Austrians have me baffled is energy conservation, specifically the following direction given - that is "open the windows 2-3 times daily in the winter for 15 minutes". Supposedly this improves their energy usage. Nothing in my learning helps me understand this and I've found no proof of this....anyone care to shed light on this seemingly strange idea?
Response to Jack Coats
Jack,
You wrote, "How about specifying how to calculate how to make the cost/benefit analysis rather than just stating doing various items are or are not 'cost effective'?"
Good suggestion -- an excellent idea for a future blog. A full explanation would be beyond the scope of the current discussion, but your suggestion has merit.
Briefly, any good energy modeling program can be used to calculate the energy necessary to heat and cool a building. By performing two iterations -- one with the existing windows, and one with the proposed replacement windows -- it's fairly simple to determine the difference in energy use between the two cases.
For homeowners interested in getting a general idea of the effect of different window choices on energy use, I suggest a visit to the Efficient Windows Collaborate website. The site includes an online calculator displaying the heating and cooling costs of a "typical" American house with a variety of window options.
Once one knows the annual energy savings attributable to the proposed window replacement, it's necessary to determine two other factors: the existing energy costs and the presumed rate of energy cost inflation. The latter number can be contentious.
Finally, an economic analysis can be done many ways. It's possible to do a simple payback analysis, a cash flow analysis, or an analysis that considers the net present value of the investment. For more information on these different methods of analysis, see:
http://www.energy.rochester.edu/efficiency/ems_analysis.pdf
http://www.money-zine.com/Investing/Investing/Evaluating-Cash-Flow-Results/
http://en.wikipedia.org/wiki/Payback_period
Response to Dave Williams
Dave,
Your point about incandescents versus CFLs is well taken. Of course, many CFL proponents exaggerate the savings attributable to swapping bulbs, because they make the elementary error that you mention. Fortunately, Michael Blasnik is aware of the difference in heat output between the two types of bulbs and has taken that difference into account.
If we were to take an extreme case, consider a homeowner who heats with electric resistance heat and who doesn't have an air conditioner. Such a homeowner is a poor candidate for swapping bulbs. But this description represents a tiny minority of Americans.
If we consider a more typical example -- a homeowner who heats with natural gas and who uses an air conditioner during the summer -- then swapping bulbs makes economic sense, in any climate.
Response to Chris Richter
Chris,
You wrote that you are puzzled about the following advice given to Austrians: "Open the windows 2-3 times daily in the winter for 15 minutes."
My guess is that the reason this is done is to provide adequate ventilation. Most existing homes in the U.S. are quite leaky; due to the stack effect, they experience a lot of infiltration during cold weather. But if a house is relatively tight, and if the house lacks a mechanical ventilation system, then the advice makes sense.
With windows it's more about the comfort than the energy
It's easy to point to a lot of measures as having a less favorable net present value on the energy savings but with windows going from U0.5 (or more) to under U0.3 there is a noticeable increase in comfort at the outdoor temperature extremes, particularly during the heating season. With better windows convective drafts go down, and the radiant loss of human skin while standing in front of the window is cut in half. The whole point of a house and it's HVAC systems art to keep the inhabitants comfortable- you can't calculate an NPV on comfort .
Similarly, while having a 3x oversized single-stage hot air furnace isn't a big energy hit the high noise, higher air flow, short-cycling & overshoots etc are a significant cut in comfort. (And as I previously posted, oversizing non-modulating boilers by 2x or more IS an energy hit, particularly on systems with low mass heat emitters such fin-tube baseboard. At 8-10x oversizing even a condensing hot air furnace takes a big hit in operating efficiency, and they're out there!) In the hot air furnace case, right-sizing it is usually getting more comfort for a lower cost system, and by not short-cycling it the equipment lasts longer- it's a triple-win.
The notion that CFLs don't ultimately save a lot of money due to the heating factor is ridiculous in most markets. Only if you're heating with ~$3.50 oil in an 85% burner in an an area with ~10 cent electricity would it be a wash on heating energy costs. In a more typical buck-a-therm gas & 15-cent electricity land the heat you get out of the incandescent bulb costs more than 2x than making up that heat with an 80% gas furnace. (And if you're heating with oil or propane and off the gas grid, adding some supplemental heating via a ductless mini-split heat pump has a very favorable NPV.)
Response to Dana Dorsett
Dana,
Once again, I'll repeat: I never said there weren't important reasons to consider window replacement. Improved comfort is one of them.
There is no argument here. If you want a granite countertop and new windows, there are plenty of reasons to install them. Just don't expect an energy payback from either investment.
Trivial Savings?
While some energy saving measures might offer only "trivial" savings in an individual home, multiply those savings by 114,000,000 (2010 census estimate of US households) and we're talking about real savings—savings that can please people with wide ranging interests: energy independence, climate change, economics (utilities save money by not building new generating plants).
For example; the 3% savings from caulking... Let's lowball a guess that on average a household spends $1000 a year on heating. 3% is $30 a year, times 114,000,000 households gives a national savings of 3.42 billion dollars. Perhaps some energy nerds can figure how much coal and gas that might save per year. Add in two more "trivial" savings of 1% each and we're getting close to $6 billion dollars per year.
Now let’s add businesses and schools and churches to the equation…
The bigger picture
I enjoy reading about ways to save money, energy, and how to be greener, and I agree with Mr. Blasnik when it comes to the cost efficiency of the retrofits and actions he discusses. The only issue I have with these types of articles is that they usually only focus on the cost reduction of the utility bill. While this is obviously very important, it does not take into consideration of the benefits of the energy savings for our Country and Planet as a whole.
What we need to understand is that the less energy we use today, the more that will be available tomorrow (I'm primarily referring to fossil fuels). By being more efficient with our energy use, we will not only have more energy to use later, but it will also decrease the amount of oil that we have to import from other Countries that use this revenue for unsavory things like funding terrorism. We all know that combating terrorism is extremely expensive, not only in dollars but human lives. While it is extremely difficult to determine how much we would save in dollars and lives by becoming more energy efficient, we should be aware that in all likelihood, it would be substantial. There are many other factors involved when calculating the true savings from energy efficiency that I haven't touched on, such as the reduced financial costs and negative health effects of producing less pollution, not to mention Global Warming.
I'm not an extremest nor am I advocating extreme energy efficiency measures, but rather I'm trying to enlighten people to the fact that there is much more to the equation in calculating true savings from becoming more energy efficient than to only determine how much money the individual will save on their utility bill alone. As Mr. Blasnik suggests, we should concentrate on the major energy hogs first and then we should work on improving our energy efficiency in areas that would pay off in the complicated "Big Picture" even if the savings isn't obvious in our utility bills.
Response to Bill Nemick
Bill,
OK, if your goal is to reduce energy use -- you still want to do it efficiently, in a way that doesn't waste money. Why advocate spending $10,000 on new windows at one house (for example), a measure with not much of a return, instead of spending $2,000 each at 5 different houses to reduce air leakage?
We all want to reduce energy use. But we might as well be smart about it. The means concentrating on measures with a reasonable return on our investment.
Response to J Chesnut
J,
I disagree with your characterization of the Passivhaus standard.
While German proponents of the standard claim that the 0.6 ach50 limit and the annual space heating limit of 15 kWh per square meter are based on a cost-effectiveness analysis, I have never seen any calculations backing up that claim. As PV arrays drop in price, my skepticism over the German claim only increases.
Certainly in the U.S., few (if any) Passivhaus buildings show the dramatic cost drop in HVAC equipment predicted by Dr. Feist. This is mainly due to the cost of the HRV, and the tendency of Passivhaus designers to specify very expensive HVAC equipment.
cost efficiency
I would like to expand on Philipp's comments on this topic.
Cost efficiency is easy to argue for some but difficult for others.
Having experts agree on its basis of being established will be impossible.
Let's recognize that the PH standard is predicated on a cost efficiency analysis for the German market (see attached graph) for homes in which a heating unit can be omitted.
I do worry about the Building America Program's strong insistence on cost efficient measures because I feel it allows somewhat conservative experts to buttress their opinions and not promote more innovative energy efficiency developments in the industry.
In principle the middle path is the best way forward.
Additionally-
Buying from a food co-op is not cost efficient if the measure is based on a food item per dollar basis. However I find buying from a co-op a very cost efficient manner of maintaining reasonable wage jobs in a good working environment for my neighbors and helping to sustain organic farming measures and all the associated businesses involved with the distribution and marketing. All in all a very positive sub economy.
I am finding driving a fuel efficient hybrid car is also very cost efficient within a car sharing program. I look forward to this sub-economy growing also in metro areas.
Response to Martin
Sure, I don't know if PHI did actual analyses. The graph I show is from the CEPHEUS book "Living Comfort Without Heat" published in 2001. As Passivhaus was presented to me this graph shows that a "sweet spot" was discovered when you can optimize the thermal envelope and the solar heat gain to the point where you can omit the heating system and invest that money into the envelope. I'm sure you are aware of this. My point is that it is a cost efficient argument if not analysis.
On the same token other entities often claim to have performed cost analyses but have made little effort to make transparent how they performed them. The release of BEopt+ I hope leads to some productive exchanges of information. (I just wish there was a MAC version of the software.)
To be clear I am trying to emphasis that 'cost effectiveness' is in its essence an argument. 'Cost effectiveness' is not an objective reality that can exist independently of subjective formulations.
I appreciate that you offered an argument about how much to insulate based on the cost of PV though I think it allows too much room to justify not pursuing further thermal performance based on the cost of an offsetting PV system that wouldn't be even required to be included.
Numbers hold the info
This is a great, and quite interesting, list of energy myths. Even surprising. While many out there may be somewhat shocked and unsure about some of them, Blasnik's point that the statements need to be backed up by numbers is an important one. Of course, there may be instances of differing results but in the end it's important for any energy specialist to take the building into context along with the potential energy saving methods. Great information.
New windows do NOT increase your home's value...
Data are Good. Remodeling Magazine's most recent Cost. vs. Value numbers just came out last week. I'm thinking I'm reading that you can expect to only recoup 65-70% of your cost for new windows on resale. That is, you will lose 30% of the money you just spent. So the argument that you "increase your home's value" is not valid either - IF you count the money you had to put in. Link: http://www.remodeling.hw.net/2011/costvsvalue/national.aspx
Low hanging fruit
Martin writes:
"OK, if your goal is to reduce energy use -- you still want to do it efficiently, in a way that doesn't waste money. Why advocate spending $10,000 on new windows at one house (for example), a measure with not much of a return, instead of spending $2,000 each at 5 different houses to reduce air leakage?"
I agree this is absolutely positively the right way to look at the issue. If we are going to have government incentives, for example -- focus them exclusively on cleaning up/greening up all the low hanging fruit -- air sealing, insulation, HVAC, storms... And until all of America gets done, no subsidizing fancier fixes. Your pyramid, Martin...
Window Quilts
Last one. Drats. My pinch pleats aren't working? Calling Window Quilts tomorrow...
sediment in water heaters
Hello: it is a myth that removing sediment from tank type water heaters saves significant energy. I think this came from a study on boiler scale, (not sediment) done at the National Bureau of Standards, eg; "According to the US National Bureau of standards, ¼” of scale build up on heating units requires up to 55% more energy to attain the same temperature." ... From a more recent (ended 1986) Gas Research Institute study on "The Effect of Water Quality on Residential Water Heater Life-Cycle Efficiency," it was concluded that even with 60 pounds of scale buildup recovery efficiency in gas heaters was reduced about five percentage points.
I'd love to see a study on boiler scale and tankless heater efficiency!
Yours, Larry
Response to Pam Kueber
Pam,
Thanks for the link to the Remodeling magazine study that shows that you don't recoup your investment when you install new windows in a house you intend to flip. There goes one more reason to consider window replacement...
Response to Larry Weingarten
Larry,
Thanks for contributing to the energy-myth list!
Insulating outlets
Back in the 1960's I lived in a mobile home at the top of a hill. In winter time when you walked by an outlet that was on a an outer wall you could feel the cold air coming through it especially on windy days. They tell me that modern day mobile homes are built better but I would not know because I have not lived in one for thirty eight years. Anyway.... I'm wondering if what is now myth had it's basis in fact years ago? In retrospect I don't think that insulating the outlets on my old mobile home would have done all that much good considering how thin the walls were and all the other leaks it must have had.
Response to Carl Belken
The information in this blog refers to houses rather than mobile homes, and air leakage patterns probably differ in the two types of housing.
It's certainly true that air leaks through electrical receptacles are the ones you can feel. Few people spend much time in their attic to feel the (usually much more significant) air leaks up there.
Energy Myths
My current collection is attached, several of which I borrowed from Michael Blasnik and others.
I have questions about the myth "Closing hot-air registers in unused rooms saves energy". The study cited was from California, and if memory serves, the homes studied had ductwork outside the heating envelope (so closing registers increased leakage of conditioned air to outdoors).
What about homes with ductwork within the envelope? Would the furnace run less with a register closed (and the door to the room closed)? A related question would be: Would the furnace run less with register closed because the thermostat was getting satisfied faster due to more heat being delivered to the room where the thermostat is located? And yes, I'm aware of potential problems from closing off registers if temperature rise across the heat exchanger (or drop across the AC coil) is close to being outside of manufacturer's specs. (Air flow outside of specs.)
Response to Jonathan Beers
Jonathan,
That's a great collection of energy myths. Thanks for sharing your list.
pocketbook and time efficiency
I am starting my house upgrading and appreciate the science based approach.
Found this blog post by trying to figure out how to caulk a window. Will now focus on air sealing the basement and then the attic.
Interesting that a post on how some projects do not provide a good economic return morphs into all sorts of non responsive disagreements.
I think the comment about windows is particularly important, a big expense. The prior owners of my house spent a lot upgrading half the windows to the "best" available when they probably would have done better by doing all the windows to a lower quality or none at all. The old windows are from the 1950s but double paned.
"furnace" filter replacement
Four and five inch media filters are pricey and there is a device by General Aire (http://www.generalfilters.com/search/G99-Air-Filter-Gage_PT60.html ) to help you determine when it's time to replace the filter. It's mounted between the filter and the blower. You zero in the gauge at the time you install a new filter and then the indicator gradually swings towards the "replace" zone as the filter loads and vacuum increases. Although this might be helpful, it seems to me if you used an actual vacuum gauge, say the 0-30 IN-Hg you have laying around from your shade tree mechanic days, you could make a more accurate evaluation. But what Hg reading should you be looking for?
Cooking pots
You mention that covering cooking pots results in "zero or trivial" energy savings. Is it zero or is it trivial? If it's trivial, of course it would not belong in a list of ways for people to save actual money on their individual fuel bills, but if every worldwide user of non-renewable energy covered their cooking pots, assuming for this purpose that they own lids for each pot and do not have to make vehicle journeys and manufacturing energy to come by lids, will there be a saving of energy over 12 months that is measurably useful?
All the furnace stuff is double Dutch to me as a European, and I'm interested to know whether turning off water-based radiator heating run from a gas-fired central heating boiler will save energy. I always turn off the radiators upstairs when I'm downstairs all day and vice versa, and perhaps I can stop bothering myself! Since most myth debunkers seem to be US based, it's very hard to get information which isn't based on running HVAC systems.
Response to Rose Rodent
Rose,
Go ahead and cook with lids on your pots, unless you are doing a sauce reduction or making maple syrup. Just don't expect that the practice will show up on your energy bill, one way or another.
If you live in a house with hydronic heat distribution (with radiators or hot water pipes to distribute space heat), then shutting off a radiator in an unused room will save energy.
Cooking #2 + human behaviour
Thanks for the response, though I still remain curious as to the actual level of the "insignificant" difference. If, for example, we assume that the entire continential US is currently cooking one meal a day with uncovered pots and that their pots are on for 20 minutes on a gas burning stove, assuming they switch to covering pots, will the difference over 12 months be closer to 5c or $5 or much more? I know it will make no noticeable difference to an individual, but I'm curious whether it makes sense as a global energy saving measure or whether it's just busy-work.
My follow-up thought is about the difference between lab measures and actual human behaviour. A lab test of a room which measures heat loss with all kinds of equipment will likely find little heat loss through a small draught or window gap. The trouble is, people are not monitoring equipment. The person who has set up his/her sofa so that it's directly in that draught will likely respond to this chill wind blowing on their person by cranking up the thermostat a couple of degrees. So although the heat loss is negligible in testing, the *effect* is a 2 degree C increase in thermostat temperature, which is far from negigible - the person is trying to compensate for his terribly cold legs/back/neck by warming the rest of him to a greater degree. He doesn't care about P values (?) or BTUs or Therms, he cares that the draught is hitting him directly and it feels cold. I have a kitchen extractor fan with a no-return valve thing in it, but it was clearly not designed for the gale force winds which rage here all winter. We refer to the kitchen as the "igloo door" as the immediate effect of opening this door is a chill wind hitting everyone in the torso. It doesn't rate much on paper as a source of heat loss, as it takes hours to lose any actual noticeable amount of temperature from the room overall, but it is likely to have a disproportionate effect on our use of home heating compared to its effect on heat loss beause the cold blows directly at us - is human behaviour compensated for in testing?
Response to Rose Rodent
Rose,
The short answer to your questions is that researchers have, over the last 4 decades, investigated the best energy retrofit measures from many perspectives, including human behavior. Michael Blasnik's data and recommendations are based on real-world weatherization programs, which compare pre-retrofit with post-retrofit energy use data. This type of data necessarily takes occupant behavior into account.
In other words, the data come from the field, not from the lab.
When prioritizing recommendations for energy retrofit work, it makes sense to list recommendations that will save homeowners money on their energy bills. You are correct that it's possible to make a different list -- a list of measures which save energy, but the amount of energy saved is so small that you will never see a difference on your energy bill. That time of energy-saving measure may make sense to environmentalists, so I am not ridiculing it. But it doesn't belong on a list to help homeowners save money.
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