Instead of triple pane windows, why not double double pane?
imzjustplayin
| Posted in Green Building Techniques on
An idea I had for putting in fixed pane windows is that instead of installing a high quality triple pane window, why not install a cheaper/lower quality double pane on top of each other? There would be an air gap so there would be 3 air gaps. The idea behind this is that it might save money while improving performance.
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Two double pane windows will probably cost more than one triple. Plus you'd never be able to properly seal between the two and evacuate the air, so the gap between the two would get fogged. Light transmission could also be limited.
Dave,
The condensation problem mentioned by Stephen is real, but it can be reduced by making the exterior window a little leaky, and the interior window as tight as possible.
The short answer is that your suggested approach is possible, and some people have done it. These windows are fussy to open and close, and hard to keep clean. Before deciding on this route, make sure that other members of your family are happy with the arrangement.
Finally, windows that operate easily are essential in bedrooms for emergency egress in case of a fire. Elderly people especially might be confused by this type of window.
Again, this would be for a fixed window so egress stuff is irrelevant. Part of the inspiration for this is that older Pella double pane windows had a removable inner pane with a rubber grommet on a corner used for this purpose as it's not tightly installed. As for condensation, why would the interior window be tight and exterior leaky? Should be the other way around? At least that's how Pella did it with their older double pane windows.
Dave,
During the winter, outdoor air is dry, while indoor air is humid. Ideally, you want the air between the two windows to be dry air (like outdoor air), not humid air (like indoor air).
Installing the inner window with a very good air seal, and leaving the seal around the outer window a little bit leaky, achieves this goal.
Martin: How do you make the outer window just leaky enough to prevent any condensation, at any time of year? Obviously any condensation inside will run down the window pane, leaving streaks that will remain after the moisture has evaporated.
The removable panels Dave mentions avoid the problem because they can be removed and the panes cleaned.
I can sort of see this as a solution to replacing windows in an existing house, although removable storms make more sense to me. For new construction, why start with a half-baked window plan when triple pane windows will almost certainly be cheaper and perform better?
Stephen,
I think it's a somewhat goofy idea, which I hope my answer made clear.
Stephen:
I have had several of the old Pella windows with the inner storm sash, and vapor in between the panels was always an issue. One, a larger fixed unit was so bad that I had to drill additional vent holes to the outside, similar to what comes with the windows, but more of them. This helped some but did not eliminate the problem. Plus, the holes are always getting clogged with dust and such, and to clean them one must remove the inner sash. This is not alway so easy on a larger window, especially if you have plants or other bric a brac on the sill.
Well the idea behind this was to save money on a remodeling project. The house has double pane windows from 1991 so they're either air gap no low-e or they're basically like those crappy pella doors. I'd have to replace the Pella doors in order to improve their performance unless pella offers and upgrade of some sort.
If the first set of windows exists already, this makes more economic sense than it does in new construction. It's essentially the same as buying a double-pane storm window. You can also buy low-e storm windows and get a lot of the same benefits for even less expense. You could even put in interior and exterior storm windows.
You can get a triple pane window, and if you want to go kooky, get storm windows. Like Charlie said. But if you live in teh USA, not the Yukon, I think the triple pane windows are pretty damn good.
The reason I'm interested in improving the window performance so much is because the house has a lot of square footage of glass and even though it was built in 1991, it costs a fortune to heat and cool. Trying to decide how to approach remodeling this house for a significant efficiency improvement. Might spend $100k on efficiency improvements. House is 6500 square feet.
Dave,
That changes everything. Have you had an energy audit done, including a blower door test? If so, what did your energy auditor recommend?
I'll have one done, also will have the ducts pressure tested as well.
Dave,
I would hold off on your window decision until you have learned the results of your planned energy audit.
Dave,
We are in the same boat on this.
I have 22 year old Pella Architect finished wood inside, aluminum clad outside windows which are built exactly the same way as Pella Proline (class action lawsuit against Pella since 2006), but with upgraded trim on the inside. The windows leak horribly and condensation builds on the inside completely around the perimeter of the upper and lower windows of the double-hung assembly, but mostly on the lower sashes of each window. There is so much condensation that the windows are rotting along the lower sash. I heat with wood only, no wet basement, all gas burning appliances and all showers properly vented to the outside, not the attic. I even added a new dehumidifier to the basement which takes a week to collect 2 gallons of water. I still HAD condensation on the windows, AND I STRESS HADDDDD!
Question: Why would a window company choose aluminum to sandwich between two insulated glass panes and then call it a THERMOPANE?? Isn't aluminum used as wire for service entrances because of its electrical/heat conductivity?? STUPID!! (THTEEWPID)
I built interior storm windows by ripping #1 grade pine 1X3's in half (but set up your saw to rip some off of all sides because quality of wood has gotten so bad that 1X3's are not all the same width), furniture screwing cross members at top, bottom, and middle where the two windows meet and lock. I rounded over the inside and outside sharp edges with a 1/4" round-over bit with a cheap Sears router. I stained, sanding sealed, and varnished all surfaces. I wrapped both front and back with polyolefin film taped on all edges with clear tape, and shunk with a blow dryer. I installed 1/2" black foam pipe insulation on the entire perimeter of the frame, and mitered the foam at 45* at the corners. I force-fit the new panels into the window jambs up against the sash stop, so no fasteners. CONDENSATION INSTANTLY GONE!! (Cost about $13.00 per 35" X 53" opening)
The foam stops airflow in both directions by double sealing the perimeter. It seals once at the interior corner of the sash stop, and once on the surface of the window jamb on all sides.
My crappy Pella windows leak so bad that three of these storm windows actually blew out of the opening due to the Pella windows leaking so badly in the high wind we had last week. I had to install spring loaded curtain rods at the top and bottom of the interior storm windows to keep them from blowing in.
I NOW BURN HALF THE FIREWOOD THAT I USED TO BURN!!
I bet that makes the green folks FEEL better.
BTW firewood is a RENEWABLE resource like corn, wheat, and all other things that are grown!!
Get your project started, it's a lot cheaper than replacing windows!!
James
Dave,
The rubber grommet in the corner of the glass is used for the operator for the blinds in between the glass. Apparently your window originally had the blinds and the removable inner glass panel to access them. I have three Pella swing doors with this same set-up. The hole is about 1/4-3/8" dia.
Back to the windows:
My son shot one of our "Pella thoropain" (purposely misspelled) windows with a BB gun when he was a youngster. Since Pella wants my first born in payment for a replacement window (bottom half of a double-hung) I decided to experiment (although I thought about the trade!).
First, I removed both the upper and lower halves of the double hung, and then installed one of my handy-dandy interior thermopane (not thoropain because there is no highly conductive aluminum spacer in its construction) storm windows in its place. I then managed to remove the aluminum cladding (slowly to allow the caulk/glue to let go gradually) without destroying it. I then noticed that the frame was "finger" jointed at the corners, glued, and nailed with one of those old square steel (rusty) nails that you find in 1800's houses. I dug the nails out carefully (from the aluminum cladded side), broke the glass the rest of the way out, pulled out the highly conductive aluminum spacer, and then pushed down on the window diagonally against the floor in order to separate the corners. I bought a replacement "thoropain" (because its the only thing available) assembly, installed it, glued the corners and installed stainless steel screws in place of the rusty steel nails. I then bought butyl caulk in strip form from Do It Best hardware (2lbs for $7.00) and putty knifed it between the new "thoropain" assembly and the interior wood. Dip the putty knife in mineral spirits and it will literally slide across the sticky butyl caulk.
I ONLY TELL YOU THIS TO LET YOU KNOW THAT I AM PROBABLY THE EXPERT ON THESE WINDOWS.
Where are you located? I can steer you through the most cost effective way to restore these Pella "thoropain" windows with the least amount of pain and cost, and how to keep them from going to HE!! again, but it's not an easy task!!
Dave,
Martin Holladay's suggestion for building a tight fitting interior window is absolutely correct. That is exactly what I did by building the aforementioned interior thermopane storm windows. He is also correct about making the outer window a little leaky so that the air temperature between the two assemblies is closer to the outside temperature and the air is dry. The inside assembly keeps the warm inside air from being able to get to the original window, so that the moisture in the warmer air cannot condensate on the colder original window panes. Fortunately for both of us, we don't have to worry about making the outer assembly, the Pella Thoropain assembly a little leaky, because Pella already did that for us with their original Pella thoropain window design!! Say THANKYOU!!
Another extremely poor design with these windows is with the plastic liners. Half of the liner is inside the house and half of it is outside the house with about a 1/2" - 3/4" gap behind it all. That means that between you and the outside, there is only about a 1/16" thick piece of plastic. Think about that for a while!!
The interior thermopane storm windows I built solve this problem also.
OK, yes, I have and engineering degree from Purdue!
Mr. Stephen Sheehy
The interior storm works great on these windows due to the original window being an extremely leaky, $hitty window by design.
If the window were brand new right now, it would condensate due to the highly conductive aluminum spacer between the two panes of glass, and it would leak air like crazy due to the air gap behind the plastic side liners, half of it being outside, and the other half inside.
Double hung windows are the least efficient window of all types including crank out and fixed, and Pella double-hung thoropain windows are the worst of the double-hung.
I guess that makes them the worst of the worst!!
But...I've proved that they are savable.
And the end product is virtually invisible unless you point them out to your visitors.
Martin
Why would you want to do an energy audit before fixing the windows?
It's like throwing more money out these damn things!
You know they leak...1991 Pella Thoropain windows suck baaaaad.
I bet no fan exists that will suck hard enough to draw a negative pressure.
Lets see...6500 square foot house, I'm gonna guess 60 - 80 crappy Pella Thoropain windows - one helluva big air leak when you add it all up!
It'll be interesting to see the energy audit result before the fix, but it doesn't make sense to do, it's not like the terrible result is going to point directly to the windows anyway. It just tells you that you have a helluva leak, or a $hitload of small ones - 60 to 80 minimum count!!
James,
A good energy audit will tell you where to spend your money first.
For many homes, the best approach is air sealing the attic and the basement; in some cases, adding insulation to the attic makes sense.
Window replacement is likely to be far, far down on the list. Of course, window improvements (like the addition of exterior low-e storms) sometimes make sense, especially if the existing windows are single-glazed.
Martin,
Respectfully, you are obviously not as familiar with these windows as I am. I have 20 of these from the 1991 era.
O.K. - If your 3 and 5 year old boys went into your stock of nails and grabbed a box of aluminum siding nails, threw them out into your gravel driveway and mixed them in with the gravel as they were playing, wouldn't you go out and pick up the ones you could plainly see first before getting out the metal detector? Its the same thing as paying someone to come in and tell you where your OBVIOUS air leaks are without doing a little experimenting on your own first!!
If you want to save some money and make your life a whole lot simpler Dave, pick a room - any room in your house, tape around the doors to that room with painter's tape (removes easily) to seal the doors. Open one window and install a box fan blowing out and turn it on high. Seal around the edges of the fan with painter's tape. Now light up an incense stick and walk around the room's trim, windows, wall cracks, and any other place you suspect an air leak from the outside, the basement, or the attic, or any other place. Hold the incense stick close to any of these places and watch the smoke. You will be able to identify the gross leaks in that room without some high cost, scientific pencil neck geek with expensive, unnecessary equipment!!
THIS IS NOT ROCKET SCIENCE PEOPLE!!
My favorite engineering rule applies here. KISS (Keep It Simple Stupid!!)
You could isolate each room and do your own energy audit on your own time schedule, without taking off work to meet someone else's schedule, and with very little cost, say a couple of bucks a room!!
If when you're done air sealing the whole house you want to call the pencil neck with the expensive equipment, go ahead, it's your money!! But I'm betting that Dave will have solved and fixed the majority of his largest problems on his own with just a little bit of sweat and ingenuity! Heck, I'll bet the pencil neck NEVER gets a call, because by then, Dave will have realized so much savings in his heat bill that his problems are no longer problems.
Just for kicks, I searched "blower door test cost". The cost must be high enough that they won't list it for fear of scaring you off. You have to call to get an estimate!!
Martin, how can a blower door energy audit tell the home owner that his attic needs insulation as you stated above? Everyone knows that insulation does not stop airflow, so how can a vacuum draw on the house tell you how much insulation is in the attic, or that you need to add more?? I guess I need to further my education on this one! Also, Dave already said that his windows have a removable inner pane... that would be double glazed.
All I'm saying is look at the obvious low hanging fruit first. You don't need a blower door energy audit to tell you where the low hanging fruit is , and it makes absolutely no sense to pay for one without exhausting your own ideas, research, and intellectual resources first!!
Hey, I'm just a practical guy with a little bit of education and ingenuity. I have an 1886 house and I've been through all the air sealing, changing outside ground contours to ensure water runs away from the foundation and installing perimeter drains to ensure dry basement, removing siding to insulate, deciding on vapor barriers or not, venting all appliances to the outside, etc. But when all that was done, my Pella Thoro-Pain-In-My-@$$ 1991 era windows were the biggest culprit related to energy IN-efficiency!!
I'm tellin' ya Martin, these windows are crap, but i can't afford to replace them, so I devised the aforementioned way to "save" them!!
Dave, good luck on your pursuit of energy efficiency! Just use your head and only make decisions that make good common (or should I say UNCOMMON) sense! There are literally thousands of people out there to misdirect you, but you are your best advocate. If you're just a little bit handy, trust in yourself that you can solve most of these problems all by your lonesome!!
James
James,
I have no problem with homeowners doing their own investigations for air leaks. But your suggested method will not find them all -- especially the most important ones (those in the basement and attic).
Q. "How can a blower door energy audit tell the home owner that his attic needs insulation as you stated above? Everyone knows that insulation does not stop airflow, so how can a vacuum draw on the house tell you how much insulation is in the attic, or that you need to add more?"
A. Home energy audits include more than a simple blower-door test. These audits include an inspection of the attic.
If any GBA readers want to follow James's suggested path -- performing a DIY home energy audit -- here is a link to my article on the topic: Energy Upgrades for Beginners.
If any GBA readers want any more information on why it rarely makes sense to invest your energy-upgrade money in window improvements -- and want good advice on what to do with old windows that don't perform very wall -- I suggest they read this artilce: What Should I Do With My Old Windows?
Alright, let's not forget the main reason for discussion here...COST!!
I can't take, nor would I want to take anything away from Martin's vast knowledge of Green Building Techniques. As far as I know, he makes a living off of that knowledge. He has been off the grid for a long time, literally!!
But when you have an elephant in the room, why worry about the squirrels? You can only get all the rocks into the can if you put the big ones in first. Get the idea here??
The 80/20 rule applies. I will not discount the fact that the blower door test will eventually find all the air leaks in your home. But I'll site that old "rule of diminishing returns" here. The big leaks are low hanging fruit and easy to find. The more you fix, the harder the next ones are to find. Martin, can't we agree that 80% of the most blatant offenders can be found using the methods I described above, or at least the majority?? And wouldn't the blower door test be more effective if you took care of elephants first?? And wouldn't there be less confusion about WHERE the house is leaking if you sealed the obvious leaks first?? It doesn't make sense to look for the squirrels when you're getting stomped by elephants!!
Martin, you replied that the method I suggested above won't find all the air leaks. You're absolutely correct!! But by saying that this method merely won't find them all, aren't you also implying that it will find the most egregious ones??
I've read probably 90% of your postings/articles here and other places, and I respect your knowledge and have learned a lot from your writings. I'm just trying to get you to steer our friend and average guy Dave here in the right direction. There is an order for doing things, and jumping into a full blown energy audit without first addressing the obvious is nonsense!!
Lets advise Dave to read up on the material you suggested above, and then if he still wants an energy audit, he can go for it!! Wouldn't you address the obvious first if you bought a pre-owned home? Or would you jump right into a full blown energy audit and pay someone else to tell you what you already know while you feel the air blowing through your foyer? It might "rarely make sense to invest your energy-upgrade in window improvements" as you said above, but at $13.00 per opening, cutting my heating cost in half, and our friend Dave here being the proud owner of a bunch of Pella Thoro-Pain-In-The-@ss windows, I'd say this might just be one of those rare occasions!
Dave, again, GOOD LUCK!!
James,
You are beating a dead horse here. I have already said that I have no problem with GBA readers pursuing do-it-yourself solutions, and in fact I provided a link to an article that gives advice on do-it-yourself home energy audits. (Here it is again: Energy Upgrades for Beginners.)
After your do-it-yourself home energy audit, you can pursue do-it-yourself basement air sealing. Here is a link to an article to guide you: Air Sealing a Basement.
Next, you will probably be ready for do-it-yourself attic air sealing. Here's what you need to know: Air Sealing an Attic.
Great!
So follow the above links, THEN get the energy audit...RIGHT???
Better yet, just answer YES or NO.
Simple, fair questions that need a straight forward, honest answer:
Does addressing the obvious air leaks in your house improve/make more accurate a blower door test result and fine tune it to point out more not-so-obvious air leaks?
Will the method that I explained above find MOST of the LARGEST energy offending air leaks?
Does the law of diminishing returns apply here with respect to size of air leaks?
If you yourself just bought a pre-owned home, would you jump right into a full blown energy audit without inspecting the home and sealing the obvious air leaks first?
Thanks,
James
Martin
I apologize to you and the world if I have offended you in any way. I am not the expert in green building, etc, but I have been relentless with improving my own home as I have with picking your brain for helping to steer myself (mainly) and others to the most cost-effective ways to improve our home's inefficiencies. Writing is much more difficult than talking because it is impossible to read the subtleties in facial expression and voice fluctuations. It is not my goal to defame you in any way, only to get to the meat with respect to the subject. I probably appear to you to be disrespectful, but instead, take me as being very direct only. I am passionate about this particular subject because Dave's windows are the same as mine, and with raising 6 kids on one income, I need to improve these windows' performance as much as possible without breaking the bank!
I have never had a blower door test or an energy audit done, nor have I witnessed one. But if you would answer the above questions, it would help those of us who NEED to improve the efficiency of our homes while keeping cost under control. I know you already said that a blower door test is a means to get there, but for many of us, improvements need to be made DIY first. What I'm trying to get to the bottom of is whether or not it makes sense, and improves the outcome of an energy audit, if the biggest offenders of waste are addressed first. It seems to me that the performance of a blower door test would be compromised or less accurate at finding small leaks if there are large ones to cloud the result. I've read your suggested links above and could not find answers to these questions.
Please let us know the answers to these questions (same as above).
1. Does addressing the obvious air leaks in your house improve/make more accurate a blower door test result and fine tune it to point out more not-so-obvious air leaks?
2. Will the method that I explained above find MOST of the LARGEST energy offending air leaks?
3. Does the law of diminishing returns apply here with respect to size of air leaks?
4. If you yourself just bought a pre-owned home, would you jump right into a full blown energy audit without inspecting the home and sealing the obvious air leaks first?
Thank You!
James
James,
Locating and sealing air leaks in older homes is a science and an art. Good weatherization contractors are always learning something new, and it takes years of field experience to get good at the job.
GBA readers like you come with varying skill sets. You may be an experienced builder who has spent years in crawl spaces and attics. Or you may simply be a new homeowner doing his best to handle a situation that is far from your usual set of skills. I don't know how much you know.
Air leaks can follow funny paths, and it's not unusual for exterior air to travel in joist bays and interior partitions. Some homes have old masonry chimneys that have been partially demolished and may not be obvious to the homeowner. Utility chases can be hard to find. Some rooms have false ceilings or double ceilings. You get the idea.
The best way to seal air leaks is to hire an experienced weatherization contractor equipped with a blower door and an infrared camera.
The second best way to seal air leaks is to be a highly educated homeowner who does his or her best to seek out and seal the obvious leaks.
James,
Q. "Does addressing the obvious air leaks in your house improve/make more accurate a blower door test result and fine tune it to point out more not-so-obvious air leaks?"
A. Not really. Blower-door-directed air sealing requires that the crew have a blower door operating while the sealing work takes place. It's certainly true that if 60% of the leaks have already been sealed by the homeowner before the weatherization crew shows up, then the weatherization crew will finish their work in a shorter amount of time (and their work will therefore cost the homeowner less money).
Q. "Will the method that I explained above find MOST of the LARGEST energy offending air leaks?"
A. I have no idea. It depends on your skills and knowledge. (See my previous answer.)
Q. "Does the law of diminishing returns apply here with respect to size of air leaks?"
A. Yes, although size is only one factor to consider. The other issue is leak location. The most critical leaks are those in the basement and attic. Small leaks in these areas can result in a lot of air movement. On the other hand, a relatively large hole near the neutral pressure plane won't leak much air.
Q. "If you yourself just bought a pre-owned home, would you jump right into a full blown energy audit without inspecting the home and sealing the obvious air leaks first?"
A. No. I would certainly seal up obvious leaks first. But not everyone (a) has my level of experience, or (b) likes to spend hours in attics and crawl spaces.
Martin
Thank you for your candid answers!
I wouldn't say that I am HIGHLY educated, just learning as much as I can from the experts such as yourself and doing as much as I can myself.
My home is a 1886 two-story with 2' thick quarry rock basement footers and walls, completely gutted 25 years ago down to the studs. The only things saved were the wooden structure (studs, joists, and rafters), and a few wood ceilings and floors. All new service entry, wiring, plumbing, drywall, siding, windows, soffit & 2' overhangs, roof, etc. Forced air LP heating/cooling and septic were the only things that were contracted out. Passed all inspections on first round. Insulated with fiberglass insulation all interior walls and between floor joists for isolation between first and second floors (I like to sleep in the cool!). Tore off old brick chimney and sealed over at ceiling line below attic. Air sealed second floor ceiling from below inside and from above in attic, then insulated with fiberglass batts.
#1 is just as I thought. A homeowner can do much of the work themselves ahead of time and let the pros find the harder to find leaks thereby saving themselves some green.
#2 is still a little surprising to me. Wouldn't sealing off one room at a time, drawing a vacuum out one window, and searching for/fixing leaks with incense stick reveal most of the largest leaks? (Switch the fan to another window to check the last window and trim)
#3 So leaks in the basement/footers/walls/rim joists etc. are critical because in order to leak air out at higher levels in the home, the cold air will come in easiest at the lowest levels in the home? That makes sense!
#4 I completely understand, and I'm very glad to hear you say that for the DIYer, it makes sense to seal any leaks you can find yourself before paying for a full-blown energy audit!! I've been all over/around/under my house looking for and sealing these kinds of air leaks.
Martin, probably the biggest thing I've ever taken away from your writings is that wet basements cause mold in attics! I had just a little mold on a few rafters in my fully vented attic with fully vented aluminum soffit in 2' overhangs with 100% ridge vents. It baffled me. After reading you, I changed the outside landscape and successfully dried up my basement. Viola! The light mold in the attic quit growing and dried up, but that was before removing the chimney and air-sealing the attic. The part of the chimney that is left is now completely inside of the heated envelope.
Thanks again for the straight answers for the DIYers out there like me.
You have to believe me though, when I tell you that the Pella Thoro-Pain windows turned out to be unbelievably bad in terms of air leaks! The interior storm windows are difficult to install due to the pressure of the interference fit between the frame, pipe insulation and the window jamb. In high wind pressure, the Pella windows leaked so badly that three facing SW actually blew out of the jambs and fell to the floor inside.
Thanks again Martin, I'm sure you'll continue to further my education on the subject.
James
The last two mornings have been 7 degrees and 10 degrees respectively.
Not a trace of moisture on the original windows or the interior storm windows over them!!
PRICELESS!!