Options for garage heat
I would like opinions regarding options for heating a garage. I know, I know, “Why the H@!! are you heating a garage?” will come to mind for many of you. Others will agree that it saves on car repair costs, improves longevity, and allows for storage of “perishables” such as paint cans, bulk canned garden vegetables, and other things wife understandably does not want in house.
Here are the pertinent factors shaping the decision:
* Super-insulated house, Manual J heat load calc gives 12,400 BTU/h (3.6 kW) peak heating requirement (for garage alone)
* Target temp ~ 45F, but may heat to 65F occasionally for working on garage projects
* Attached garage, 2 common walls with house, two 8′ insulated overhead doors
* Nat’l gas rate is $0.84 per therm
* Electric rate of $0.087 per kW, or 3 times the cost of NG for equivalent energy
* Could get rate of $0.042 per kW if opted for Energy Control Program (meaning, PoCo could restrict electric use during times of exceptional demand)
So, options are:
1. Direct vent natural gas garage heater, e.g. Modine Hot Dawg. Problem is, tough to find units smaller than 30,000 BTU/h. Thus, short cycling, premature wear, and potential problems with condensation.
2. Electric resistance heat. Can be appropriately sized, but operating costs higher. However, if I went with Energy Ctrl Prgm, not much higher, but risk having power absent for up to 12 hrs, or more, meaning perishables could perish.
3. Mini-split. Lower operating costs, but higher initial costs.
4. Unvented NG heater. Moisture issues from combustion. Garage is not leaky enough to accomodate, I fear.
5. No heat. Just use a portable space heater when needed.
Another part of the option equation may be recognized from a prior post… the house is under construction, and I’m thinking of proceeding with garage heat, knowing I could pirate that heat source for the house to make the working environment at least a bit more comfortable this winter.
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Must be a heck of a garage if it has a heat load of 12.4KBTU/hr with an indoor design temp of 45F! Is this garage at altitude in the Brooks Range or something? (Can't be- the electricity & gas is way too cheap.) The shores of Hudson Bay, mayhaps?
What is your 99% outdoor design temp?
Sorry, thanks for alerting me to the inconsistent data I provided. The 12,400 BTU/h is at indoor design temp of 70F, outdoor temp of -13 F (values used for the whole house heat load calc). I simply broke the garage out as the program (Taco Heat Load Program) does a room-by-room analysis. Your alert recognition of the inconsistency highlights my conundrum with the Direct Vent NG heater option, though, as my actual heating requirements are likely to be even further removed from the 30K BTU minimum sized unit!
Kent,
You've requested opinions. I'll pass along my experience in case it applies:
I know of two garage heaters near us (Chicago area). At one, a neighbor installed a gas furnace in his garage. It's quite grand. I don't have the specs but it is wall mounted with a dedicated natural draft exhaust. He had to extend the gas line into the garage to supply the heater. There's no ducting. It just heats its immediate surroundings. He confidently states he can hold 70F throughout the garage with no sweat. Very macho. It's a 3-stall garage. He did no special insulating, however. I believe he has a basement shop as well. In the garage he has a work bench and I've seen him doing brake jobs and oil filter changes and sundry repairs in fair weather when one garage door is open. The heater does not protect against freezing as it is manually controlled. It turns out he does a fair amount of repairs and building projects in the garage BUT ONLY RARELY USES THE GAS FURNACE.
Our house is vintage 1989 and definitely is NOT super-insulated. I occasionally do projects that are big enough that our basement shop is too crowded. So, in warm weather I work outside. In cold or wet weather or at night, I usually use the garage. It's a finished 3-stall with bedrooms overhead and one wall shared with the house proper. I was interested in energy savings and decided to insulate the garage beyond the existing drywall walls. I also did some improvement of the garage door seals but, let's face it, there's still a pitiable amount of leakage possible. I find, however, unless there's a strong wind, the leakage is much less than I expected. I used magnets to mount 1" polyiso on the pedestrian door and house access door, and installed acrylic over one door window. I used clear plastic to cover/insulate two casement windows that admit sunlight. The big job was the garage doors. I created a light wood frame, installed a dual layer of 1" polyiso (2" total) and held it in place with long screws and washers (no glue) and covered it all with FRP sheet.. The insulation is relieved to allow the door segments to travel on the rail guides without interference. I had to upgrade the openers from 1/2hp to 3/4hp and beefed up the torsional springs. The weight and torsion balancing is a little tricky but it works.
The result was a garage that was noticeably warmer in cold weather and cooler in warm weather. It's about 5F+ warmer than ambient during cool weather. I've used the garage for winter construction since then and wore a jacket but didn't need additional heating. I don't do much auto repair any more but with coveralls, it's doable in 25F outside weather. We've had no loses for freezing since the insulation was installed.
So, why do I tell you all of this when you just wanted input on a heater? Well, I found once I did the insulation, I had little or no justification for a heater. The overhead bedroom benefits from a warmer garage in winter, and the garage is a more civilized space. Since you may want to improve garage sealing/insulation once your new heater is in, consider starting there and then decide what heater is needed (if any). If your garage is also "super-insulated" ALREADY (as is your house), your #5 option may be worth trying. Then, see how much you actually use it.
WD - sounds like quite a garage undertaking, and your "moral" is well-taken. I may be able to get by with even less heat than I'm thinking I'd like, further villifying over-sized direct vent NG options.
Kent,
In 2002 I built a detached 24'x26' 2 bay garage/workshop in CZ 6b. I installed 2 parallel zones of 1/2" hePex in the concrete floor. For the heat source I used the smallest on demand Rinnai propane direct vent WH available. It is set up with a Taco pump feeding the input and a manual bypass valve for circulating without the Rinnai in the loop. Control is just a timer that runs the pump at intervals for a short period. There is no thermostat. The Rinnai fires up when the pump runs due to the flow. It wouldn't take much to hook this up to a solar panel too. The radiant floor buffers nicely and does a good job of warming the vehicles and tools. I'm doing the same in a new detached garage that I'm building at a new house because I like it so much and it's always worked great. Very simple and requires very little room. Just thought I'd share that since you asked for opinions.
Chuck - nice, simple yet elegant heating option. Unfortunately, my slab has already been poured. Could do something similar with baseboard radiant, I suppose? Except I'd loose the benefit of the concrete thermal mass, which I agree is wonderful! Have PEX radiant w/ NG boiler heat in detached garage/shop. For this application, looking for cheap, simple option to keep temp in garage above freezing for 95% of time, and at comfortable working temp of 65F for a Saturday afternoon every once in a while.
I recently added insulation in my attic of my garage - have been very happy thus far with my 30° above ambient garage (...soil is still warm i suppose).
For very sporadic heating - i really like gas infrared heaters. They do have slightly higher efficiency models. But just love that you can turn them on and within a minute its nice and 'warm feeling'.
can't imagine your garage doors are that tight... how did you model that? tested air leakage?
I just put a box fan in my garage door to house when I do car work (along with an electric IR heater right near by) My 97% eff furnace is my best bet for heat... :)
Also many theromostats let you adjust cycle timers or temperature deadbands etc to prevent cycling. My bet is a small gas heater would be fine. Cost for a off peak electric meter will add to your costs pretty good i think? Or do they just do a wireless lockout (like with AC units)?
I agree that:
1) Insulate and that will get you to the tolerable level and protect from freezing, and
2) For temporary heating to make it more comfortable for a saturday project, IR heating is great, as it instantly make you comfortable, without needing to heat up all the junk stored in the garage.
But I would use an electric IR heater to avoid fumes from the gas ones. Just the simple kind with a quartz tube and a reflector--no fan--so that almost all the heat comes out as radiation. If you want to go all out you can mount those on the ceiling so there's IR heat everywhere, but you can also get a portable one and just put it where you are working.
Good suggestions, Nick and Charlie. IR heaters would fit my bill if I were after personal comfort. The heat in the attached garage is to protect canned goods, and make my wife's car - and wife, when she gets in said car - happy. So, really looking for low level ambient heat of air and objects... at low cost.
If you just scale the 70F & -13F design temperature heat load to 45F & -13F, you end up at a heat load of 8680 BTU/hr, before correcting for the actual U-factor of the garage door, which are almost always ridiculously exaggerated.
Call it 10,000 BTU/hr, or 3000 Watts, probably not more, and that may still be high, if you tighten up the place.
Is -13F a realistic 99% design temp, or is the coldest temp seen in a typical year? Got a location so we can verify the temperature data?
A 30K heater isn't overkill for a 10K design load if you normally keep it at 45-50F and want to bring it up to a more comfortable temp in a reasonable amount of time. Non-condensing air-delivery gas-burners are going to have a problem at 45F indoor temps, but a condensing version could work. But ceiling or wall-bracket mounted gas radiant heaters don't have that problem, and would be far more comfortable while the place is still coming up to it's temp, since it is heating the objects in the garage (including the humans) direct, not the air first.
Just one vendor selected at random from the web:
http://www.heater-store.com/Mr-Heater-MH25NG-garage-heater.htm
There are many others with different output & form factors, but 25-30KBTU/hr of radiant heater isn't ridiculous for the application, even if it would be for a forced air solution.. It's a common solution for large warehouse heating, since comfort can be achieved at lower temperatures, limiting the comfort shock & shortening the comfort recovery when large doors get opened & closed.
Kent , is this a detached garage and what type of heat are you employing for the home ?
Here's another idea...not sure if it's a good one: If the goal is making getting in a car more pleasant, what about a block heater for the car? Then the car's heater works more immediately? But maybe plugging and unplugging is too much trouble?
Charlie,
Read what Kent wrote -- twice. "The heat in the attached garage is to protect canned goods."
Thanks for all the input, everyone.
Dana - I'm in SE Minnesota, climate zone 6. Used Rochester 99% winter design temp of -13F from energystar.gov design tables. I guess I knew the load would scale in linear fashion as a function of delta-T, but I did not consider that there could be valuable reasons for oversizing equipment. And yes, I elected to "fudge" my OH door contibution to heat loss by increasing the infiltration a bit.
I have a chance to get some real-world data, and think I might just do that. I'm going to place a 1400W space heater in the garage, and see what temp the inside air equilbrates to. The temps over the next 48 hours are forecast to stay in the 20's, so if by heat load calculations are to be believed, I should find the temperature inside to be low to mid 50's come Wednesday. If that turns out to be so, I'd be satisfied with a unit producing 10,000 BTU/h, as it would theoretically be capable of a 60 degree plus delta-T running continuously. So even during 25-below nights we'd stay above freezing.
However, it's nice to hear that even a 30K BTU/h heater isn't patently absurd. Maybe I'm overthinking this...
Chuck,
I would be forever grateful if get me some pics of your heat supply, Could it work with a Tank version water heater? My radiant is not hooked up because I have been hoping to find a simple system like you describe. I am so happy to hear that someone else has had success with this....I was beginning to think I wasted my time with the pex loops.
Kent how did the test go?
FWIW I found that Garaga Garage doors seal up fairly well...they have the best jamb weather strip I have ever seen. My gagage tested at 1.8 ach before drywall went up. I found no noticeable air leaks at the 16' door when blower door was running, I did however find other air leaks.
I also agree that just having it insulated so well is makes it comfortable enough for work, and keeps it above freezing for paints, and for snow melting off cars. I plan to use small electric heaters as needed, till I can figure out the radiant
Dirk,
The photo shows how I have it set up now but it doesn't need to have all those pressure and temperature gauges, and flow meter. It's experiment apparatus. The basics though are the timer, circ pump, water heater, bypass valve, air eliminator and expansion tank. Not shown because it's further to the left near the loop manifolds is the fill/block/bleed valve set. A water heater tank might work but you'd want to keep the supply/return dT at least 10F and preferably 20F so the run time would have to be set accordingly. Please note: This is just my stuff and I'm a hacker not a plumber.
Firstly check out the Garage Journal forums, they are the end all be all of garage awesomeness on the interwebz. There are people on there who do a low level heating of their garage in the winter and many are very willing to share their experiences. You may want to consider bumping up your temperature to 55-60F as the warranty on the heaters may not be valid operating below those temps.
Secondly: Oh goody you have an attached garage. Boy those things are convenient ain't they? What I worry about with an attached garage regardless of if it is heated or not is the amount of air infiltration into the house from the garage. There was a Canadian study a few years back that measured indoor benzene levels in houses with attached and detached garages, and what it found is that attached garages caused enough of a rise in benzene levels to be of some concern. Benzene is a chemical pollutant that basically evaporates from gas and oil stored in the garage, and also enters the garage through unburned hydrocarbons in vehicle exhaust. Basically to counter act this the garage needs to be at a lower air pressure than the house is. That means you really need to add a continuous exhaust fan to the garage. By my calculations this doesn't need to be big, something around 15-30cfm is all that should really be needed, but I haven't backed that up with any tests to verify. The actual cfm needed should be something that is verified by using a blower door (or window) to depressurize the garage and checking that depressurization against the house that is in likely operating conditions, unless there is a building scientist (or someone with better access to the literature than I have) is comfortable with recommending a cfm for continuous exhaust venting of the garage.
Chuck, your instrumenting is interesting. I can't see from the pic what the gauges are and what they are telling you. Could you list out the flow meter and the digital temperature items? I have used in the past quite a few dual temp/pressure gauges like you have and that's about it. I have found the gauges not to ever read close to the same pressures or temps... they seem not to be accurate but do at least inform differences at their point of use. Anyway nice clean set up even though I would not have known or done some of what you did but there are million ways to pipe boilers.
Since we are discussing "garage heating " ,
how would you guys handle the humidity and temp problem that letting in a cold and dripping car brings during winter season in heating climates?
Runing a dehumidifier that drains itself seems a first step ..
still brining a block of ice inside a conditioned space needs to be addressed.
My personal garage is attached, but insulated from the house ( supporting icf wall in between )
and i've installed doors as it if were exterior doors ( sealed as good as a good front door )
Have yet to bring in a cold car ( garage is still full of junk ,tools and building materials )
I know that most folks around here like to have attached garages,
but half of them aren't for cars ...usually bikes,wood,motorcycles,lawnmower etc..
Not sure how i would design a garage in an ultra-efficient house.
Probably only a car port ...
keeping a garage @ ~ 5c which is attached to a house but insulated from it brings any unknown challenges ??
the average deltaT @ 5c is almost half of what it would be @ 19-21c locally.
What do you guys think of a "car shower" to help remove slush and bring up body shell temp
of a cold slushy car that was just brought it the garage ?
( the tap temp water flushes away in the drain with some of the sub freezing shell temp? )
AJ, the big long term problems with Benzene are anemia, leukemia and it may cause non-Hodgkin's lymphoma and multiple myeloma, it likely also plays a role in things like asthma sensitivity, sick building syndrome, etc... Benzene is a known carcinogen with no know safe threshold level. Benzene is also not the only pollutant to be concerned with, but being heavier than air, and having a decent ability to easily be detected, it's a good but imperfect indicator of garage sourced pollution in homes with attached garages.
Donald, I just read up on benzene, interesting. Number one source ten times other sources is smoking. Glad to be a non smoker.
I do like the idea of late to (to not tooooo or too) install an exhaust fan in a garage to give it slight negative pressure and to not run a car inside the garage. Another good reason to buy an all electric vehicle too! Richard Beyer... notice the use of too not to. Another little hint, work on your (you're verses yours) as much as you post how foam is about to kill off the entire human race. I may have to work on less italics and parenthesis use.
Edit add... Donald, thinking a bit, I do know of one person each who have in mid life came down with most of the sicknesses listed related to benzene. Glad to see the EPA working to lower the levels.
AJ,
Here's a labeled photo with descriptions. The piping was remodeled to replace a Stiebel Eltron DHC 8-2 electric that had insufficient flow rate. I wanted to see pressure drops accross the heater and the floor loops hence the extra pressure gauges, and calculate the energy transfer hence the delta T and flow meter.
1. Another gas valve up there.
2. Pump discharge 0-30 psi
3 & 5. Pasco temp gauge
4. Azel Digit-Stat in/out temp
6. Heater discharge 0-30 psi
7. Pump suction 0-30 psi
8. Burkert 8035 flow transmitter (found on fleabay cheap)
9. Taco 009-F5 (a Taco dT controlled variable speed would be interesting)
Did my experiment with the electric space heater in the garage. Took temperature readings twice daily for ten days, with 1400W space heater running continuously ($2.78 per day). Compared NOAA recorded temps for same 20 data points. Average outdoor temp ((Sigma:Temp)/20) was 19F. Indoor average 43F. So, 1400W, equals 4777 BTU/h, provided 24F delta T. Extrapolating to target garage temp of 45F, with outdoor design temp of -10F, means I'd need almost 11,000 BTU/h. So, I learned my garage is not quite as efficient as the TACO heat load calc software predicted, but I've only done the wall and ceiling spray foam so far. Still have to seal around the window, service door and put up airtight drywall.
So, what soes it mean? Maybe as suggested by Dana and others 30K BTU garage heater is realistic. However, the points made about "pollution" from attached garage merit thought. I'm not worried about humidity as Jin Kazama expressed. I suppose if I stored my tools....
Kent you speak of Benzene. You said your home is super insulated. What did you use to super insulate your home?
Richard - Exterior double stud walls with 3" ccSPF against exterior sheathing. Balance of wall space filled with netted and blown fiberglass to create R40 wall. Gaskets and accoustical sealant under sill plates, with all wood/wood interfaces caulked along seams (e.g. between king & jack studs on exterior, sole plate and subfloor interior, top plates, etc). Airtight drywall planned (not taht far along, yet). Ceiling spray foamed to backside of drywall, with all non-essential penetrations eliminated. For example, placed smoke detectors on interior wall rather than ceilings. Attic will have R60 blown insulation added on top of ccSPF.
Garage not so tight, though. Attached garage has 2x6 wall with 4" ccSPF, though still intend to caulk and seal with canned spray foam every place I can identify as being possible infiltration location. I even planed door frames so that garage door sat as flush as possible. Regardless, as data reveals, garage not ultra energy efficient yet.
On the other hand, the house heat load estimations are being validated. The TACO software Manual J gave me an estimated heat load of 33K for house. Thus far, all I've done is the spray foam. I've moved the 1400W space heater into the house, and placed another 1500W unit in the basement. Five days of data indicate interior staying about 20F warmer than outdoor temp, indicating heat loss of under 40,000 in house not yet fully insulated (but also lacking few key penetrations, including dryer vent, bathroom fans and range hood.)
Donald, garage venting I am for. How many people have had a problem with benzene and what sickness do they get?
As to the picture posted of garage heat there are mistakes in some of the set up. One for example is the incoming gas supply. Drips on the last 90 turn are preferred. The shut off valve should shut off gas supply and then after that toward the heater should be the union. There are a few more changes I would make. And thanks for explaining the reason for all the gauges.