Best heat/insulation for living space above a garage

4 years ago

last modified: 4 years ago

Hello, I am building a Master Suite (bedroom, walk in closet, bathroom) sitting room and laundry room over a 3 car garage and am wondering what's the best method to keep these rooms comfortable. I live in US climate zone 5 (Pennsylvania). (I've been scared by lots of people mentioning it will be cold in the winter and hot int eh summer)

Garage is not heated and will have 2x6 walls (R-23 Rockwool) and potentially a 2-3 inch continuous insulation outside the wall sheathing (approx an additional R-10). House (also 2x6 walls with R-23 and potential continuous insulation) is currently heated/cooled with a 4.5 ton geothermal unit. I'm not sure if the geo unit will be able to hand an additional 1000 sq ft for heating and cooling, and it will have to make a pretty long run to get to the farthest room (maybe 40 feet) (anybody know about how many sq ft a 4.5 ton unit can heat/cool?)

I was thinking:

1. Installing Rockwool insulation in the floor joists. They are 2x12s, so I can get two of the 2x6 batts in (R-23 each) giving me R-46. Will this be enough to keep the floor warm/rooms comfortable? (I could probably add another 2 inches of continuous insulation below the garage's drywall ceiling if I need more R value - that would get me to R-56.

2. Insulate the garage ceiling as mention above and add electric radiant heat to the floors above the garage. Seems expensive to install, and I'm wondering how much it will cost a year to run. (maybe the geo will just need a little help in the cold months)

3. Insulate the garage ceiling as mentioned and install ductless mini splits in the rooms to provide heat (and cooling). I'm thinking install cost of 5 mini splits will be about the same as the radiant floor heat? But is this cheaper to run? Will I need to extra cooling capacity as well?

4. Put in a separate central heat/air for to handle all of these rooms (if the geo isn't sufficient), not sure I like the look of mini splits...

5. Heat the garage to 50, to 60 degrees. Seems like a waste of energy/money as I rarely use the garage. But it may not be too expensive - I've never seen the garage go below 40's except perhaps in rare negative temp days. I've never seen it below freezing. (The water from the house will potentially run through the garage ceiling - should the garage be conditioned to prevent them from freezing, or will the R-46 ceiling be good enough if the pipes are kept closer to the livable floor vs garage ceiling?

I could heat this will a mini split, a 220 electric heather, or a pellet stove (are pellet stoves a pain? can any of the heat from a pellet stove be transfer to the upstairs portion?)

Any help is appreciated!

Featured Answer

weedmeister

4 years ago

It sounds like plenty of insulation to me.

I would not necessarily heat the garage unless I intended to use it as a workspace. Just keep the doors closed. And maybe have insulated garage doors.

I would not used electric radiant to heat the space, especially with geothermal. You might explore hydronic with the geothermal if it can handle it. Otherwise, I'd look at a heat pump minisplit. You can have a single compressor outside with multiple heads inside (plus a refrigerant distribution box). That would solve both heating and cooling, and would be separate from the geo system.

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Comments (10)

decoenthusiaste
4 years ago
Try a mini-split unit. Get someone out to give you an estimate. My daughter installed one in an over garage closet to cool it and control humidity in Texas. I'm sure it would heat as well but the bonus room already had HVAC installed; it was just the closet that was a problem.
tatts
4 years ago
Call an HVAC contractor (or your geothermal guy) and take their advice.

Do nothing until you get the insulation and HVAC sorted out. By a professional, not by the internet.

Call them tomorrow. Done. Simple.
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OK, so if it's a garage, I assume that you don't want to heat that space so you want to insulate the top (under the slab). Again, typically I think extruded polystyrene is the right material for that although I'd be concerned about pressure from the vehicles on the garage floor. Never heard of using an earth box as a heat exchanger. Seems like there's risk of waste unless you insulate the box really well. Also, I don't really like the "one-way" engineering of an earth box (though I've got one of my own, not yet in service, and to be used for space heating, not for heat exchanging - my box is 12 in to 17 in deep and filled with compacted soil, though the pex tubing is embedded in a sand layer at mid-height of the box). If the pex ever gets damaged in that box, there's not way to fix it unless everything is torn out and you start over. I guess this is less of an issue for you since it's a garage. For me it's a finished family room. I didn't use any aluminum wrap - I don't see how that would help much - the heat still needs to get from the sand to the tubing and I don't see that anything will facilitate the process much. The reason why the book you have doesn't give specifics is because there's too much variability in the concepts. Again, a heat transfer calc needs to be done. Why don't you head over to the UC mechanical engineering department and see if there are any ace heat transfer students around who might run a quick calculation for a little extra cash. I think you could find a grad student in search of some extra beer money. I'd get serious with the idea before constructing.
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Thank you both for your replies. I am in Michigan. John Manville makes a 2 inch foiled faced rigid foam board. I am concerned about the warmth being/staying in the bathroom not the garage. So perhaps because of my climate I could just use plain 2 inch XPS. But I was told to use the foil faced because it is fire proof. Mike and energy rater the garage temperature is the same. I wanted to use the foam board to reflect back and keep the bathroom warmer. The insulation company told me to place the foil face into the wall, that way any heat in the bathroom will reflect back into the bathroom. Boy this is so confusing to me. There is a heat vent in the bathroom under the vanity. I realize what you are saying about the supply problem in the bathroom, thank you for that. Interesting that I wouldn't see a difference in temperature in the bathroom with putting foam board on the garage side of the wall. I just had blown in cellulose in the attic and that is what the insulation guys told me,...to add the foam board to the garage wall that shares with it the bathroom wall. The other issue I have is the bathroom fan. The insulation company added the cellulose up to R49 and air sealed the attic...it is warmer on my second floor. BUT here is my question...The bathroom fan a new Panasonic when I first turn it on there is a whoosh of cold air that first comes out of it. I realize that there could be cold air sitting there at first on the attic side. BUT I felt it last night with the fan turned ON and there is a bit of cold air that circulates at the top of the fan. I stuck a tissue up there and it definitely sucks the air out of the room but it is weird. Needless to say it is it is chilly in the bathroom when taking a shower until the bathroom heats up from the steam of warm water from the shower. . Does anyone have any thoughts on that?? The duct from the bathroom fan is vented out to the roof and is an insulated duct. The only thought I may have is that it is not properly air sealed on the attic side. Any thoughts or ideas are most greatly appreciated. I am a new homeowner and am new at learning all of this. Your patience is most greatly appreciated.
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For some reason, I see a lot of garages without insulation, and without any sort of venting on the roof. Without insulation, venting can make a big difference in a garge, especially in a hot climate like Arizona. I'm guessing you already have several vents around the perimeter of the garage, down near the floor. The addition of a roof vent or two, up near the peak of the garge roof will allow a lot of heat to escape, and pull in cooler air (if there is such a thing in an Arizona summer) from down near the ground. The garage still won't be cool, but it won't be an oven, either. A roofing company or a good handyman could cut in some vents in less than an hour. By the way, if the insulation company was quoting you a price for insulation blown into an attic, that's a pretty fast and simple job. Because garages seldom have attics, rigid insulation or fiberglass batts needs to be fitted between the ceiling trusses (or do I mean joists? - never quite sure) -- a much more time consuming process. Hence, one possible explanation for the differences in cost. James
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Rooms above unconditioned spaces are always hard to conditon. I usually recommend foam (and no, Gary don't care to go there...not a foam person in most cases!) in these applications. Usually my foam recommendation is for existing homes on piers with no working room to do the following install. If you install batt insulation, use unfaced batts and oversize the batt. instead of R30, install R-38 to keep insulation in full contact with the flooring to avoid any future condensation issues as the batt settles. Use a foam sheathing board to the bottom of the floor joists and finish porch ceiling as planned. Cost will be less than foam insulation, insulation value will be achieved and the foam sheathing boards will stop any air flow through the insulation that would lessen the R-value of the batts. Same performance as foam insulation. In my area people complain of these and bonus rooms over garages staying hot (hot humid climate here with 9 month cooling season!). Insulation isn't enough - air flow has to be stopped before these rooms can be comfortable. Unfortunately many a/c companies will oversize systems to try to achieve this, at a higher install and operating cost to the homeowner..and usually it doesn't work. Oversizing can lead to many issues. Best of luck to you! Hello Manhatten42..how have you been? Is vapor barrier location ok for my suggestion? And folks if you don't know Manhatten42..he is a great resource, excellent code specific info.
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Elmer J Fudd
4 years ago
There are plenty of homes in plenty of places where under the living space floor is air of outdoor temperature.

The key is to make sure between the garage ceiling and living space above is well sealed from an air infiltration standpoint (you need that for safety because it's a garage anyway) and adequately insulated. Spray foam of the right kind properly applied to the necessary thickness will do that. For illustration, the attics of houses, maybe yours too, is outdoor temperature in winter. It's not a problem if the air sealing and insulation are properly done.

There's no need to heat the garage. An HVAC contractor will give you equipment choices but your builder needs to be on board to properly seal and insulate the space.
deb s
4 years ago
Maybe do a propane heater if you can hide the propane tank well- possibly on the side of the garage? -- maybe look into the https://www.rinnai.us/product/vent-free-fan-convector/fc824p And spend the $ on radient floors in the bathroom well worth it
wacokid
4 years ago
As far as the insulation, you can’t do any better then what you have planned. Might be even more than you need. Good luck.
decoenthusiaste
4 years ago
How low do winter temps get where you live? Propane doesn't do the job when temps fall into the teens and twentys.
D H
Original Author
4 years ago
A typical winter is single digits to mid 30s. Do propane fireplaces work in these temps?
decoenthusiaste
4 years ago
Depends on whether they're high powered with blowers or just decorative.
katinparadise
4 years ago
If you have rooms over a garage, most building codes require that the drywall on the ceiling be 5/8" type x for fireproofing reasons. Be sure to check your local codes to see what you need to do.

Best heat/insulation for living space above a garage

weedmeister

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Best heat/insulation for living space above a garage

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