Insulation/heating ideas for suspended slab garage (long)

[Proud Highway]

This is my house that was completed in Dec 2012.

It has an insulated two car garage on the ground/street level which sits on a ~10" suspended slab. Underneath, in the same footprint, is a similarly sized, but unfinished space with a 8'2" ceiling aka "lower garage." The lower garage has a single 9' wide insulated garage on its side.

I wanted the capability to pull tall vehicles in the lower garage so I put in the tallest garage door I could (I also wanted to avoid ducking around lower hanging door tracks inside). The tradeoff is that there isn't enough room to insulate the concrete ceiling of lower garage as the door hardware is 2" from the ceiling in many places.

The winters in Northern Utah are cold and I'd like be able to use the lower garage all year for a shop/man cave. I've wrestled with various ideas about how to insulate the ceiling in the lower garage because I'm told that concrete has a R-value of ~ 0.08 per inch. Most of the ideas involved modifying the garage door for more clearance or switching out the door for some swinging "carriage house" doors.

The other day I had another idea I wanted to run by the collective wisdom here. The "upper garage" is insulated and since there is living space above the upper garage its ceiling is copiously insulated. So rather than insulate the ceiling of the lower garage, could I just insulate the walls (which are bare concrete right now) w/ 2x4 construction and rely on the insulation of the upper garage to capture the heat?

I realize that the area to be heated would be effectively doubled with this plan, but given the poor insulation value of the suspended slab wouldn't this be similar to heating a 24x24 garage with a 19' ceiling? (i.e. 8' lower garage + 10" suspended slab + 9' upper garage) One upside is that the upper garage, which is a little cold in the winter, would capture the heat from the lower garage when I was down there.

Any thoughts or input on my idea or other proposals would be greatly appreciated.

My intent was to put in a gas operated modine/reznor/HD heater in the lower level. Is that possible with an 8' ceiling?

 

[Haywood]

Yes, it will work. I have the same setup and run a modine heater. The upper garage is usually a few degrees cooler (I keep the lower at 54, upper garage usually is 45-50 according to my truck's thermometer in the morning). As far as insulation, I have 2" of styrofoam on the outside of the lower level, upper level is 2x6" insulated the same as the rest of the house.

The only drawback I've noticed (if you want to call it that) is that when you park your car/truck in the upper garage and its got snow on it, the snow melts off and the garage gets really humid with a lot of condensation on the windows. I ended up getting a dehumidifier that I turn on if I park the truck with a bunch of snow on it. I have a floor drain in the upper too, might be even worse without it.

Here's the only picture I can find where you can see the heater, it really doesn't hang below the garage door tracks at all.

 

[HoosierBuddy]

I think your plan is good.

Regarding the issue with snow melt...Floor drains are the way to go.

Man, I'm glad I put in drains in mine!

Phil

 

[Proud Highway]

Thanks for the feedback.

IIRC, the code in my neck of the woods was amended to prohibit floor drains in garages. The thinking is to discourage chemicals from being introduced to the water/sewer system.

 

[Gunslinger99]

I have a very similar setup to yours and I also live in northern Utah. We finished our build in September of 2012. I love your idea of putting the heater in the lower garage and having it heat both levels.

What size of heater are you looking at going with? I've been reading about heater size and am getting kind of confused. Some say its ok to oversize the heater and others have said to size the heater correctly to your space. Each heating application can be different depending on building construction, climate, how much time you intend to be in there etc.

I found a formula for calculating the btu's needed for a garage. It says to take the Square footage times the ceiling height which will give the cubic feet. You then take this number and times it by 2, 3 or 4. Where 2 is very well insulated, 3 average, 4 no insulation. This supposed to give you a good estimate for btu's. not sure how accurate this is. Anyone have comments on this formula or a better way to calculate btu's?

My garage is 1365 SF on each level. Each with 10' ceilings. 8" of spandeck and 4" of concrete sandwiched between them. So 21' for ceiling height. If I use the formula above and your idea of heating both garages from the lower I get 85,995 btu's. 1365*21 = 28665 * 3 for average insulation = 85,995. The lower garage has no insulation currently installed other then r14 rated garage doors (two at 10'x8') However, the walls are 12" thick concrete with probably about 60% of it burried in dirt. the other 40% for the common wall shared with the house. The upper has r19 in all walls and r30 in the ceiling. I intend to insulate the lower garage at some point. Although I'm not sure if I should with so much concrete surrounding it.

So, will a garage heater rated for around 85000 btu's be sufficient for my situation? I found a couple of used 200,000btu garage heaters for sale. But I think this may be overkill? Thoughts please.

It is not my intention to high jack your thread. Forgive me if I have. I'm hoping my questions may help you figure out the correct size of heater for your garage as well.

Thanks...

 

[ForceFed70]

I think your idea is good so long as the heater can keep up with the demand. Controlling temp in the upper garage will be difficult this way however.

Could you not do spray foam insulation on the ceiling of the lower garage? 2" by the tracks will actually give a pretty good R value and you could have them spray it a little thicker (3-4") wherever you don't have clearance concerns.

 

[Gunslinger99]

I think your idea is good so long as the heater can keep up with the demand. Controlling temp in the upper garage will be difficult this way however.

Could you not do spray foam insulation on the ceiling of the lower garage? 2" by the tracks will actually give a pretty good R value and you could have them spray it a little thicker (3-4") wherever you don't have clearance concerns.

How would he figure out if his heater will keep up with the demand?

 

[ForceFed70]

How would he figure out if his heater will keep up with the demand?

Heat loss calculation. There are a few online calculators available.

 

[Proud Highway]

I was told a reasonably insulated 2 car garage in our climate could be made very comfortable w/ a 40k BTU heater. Since I'm 2x2 I would probably consult with the HVAC pro before ordering (he'd have to green sticker it anyway) but I'm guessing 80k is close. Good call on the 10' ceilings.

The spray foam idea is interesting--I will look into that. I'm starting to regret my not taking a little more proactive role in overseeing this part of the project.

One solution is to have the bottom section of my garage door replaced with a shorter section and have the door installation lowered 3" so it totals 5"+ everywhere else. Then I'd be home free except except for trucks/SUVs.

 

[Gunslinger99]

You won't want to insulate your ceiling in the lower garage if you are only going to use a heater in the lower garage to heat both levels right??? I would think it would stop too much heat from moving upward.

 

[Gunslinger99]

Will a 200k btu heater be overkill for our garages and trying to heat both levels?

 

[ForceFed70]

You won't want to insulate your ceiling in the lower garage if you are only going to use a heater in the lower garage to heat both levels right??? I would think it would stop too much heat from moving upward.

My understanding is that the OP wanted to only heat the lower garage.

Will a 200k btu heater be overkill for our garages and trying to heat both levels?

I would think 200K would be OK if it was all one level. But with heating 2 levels the heater would heat the lower room too quickly and result in a lot of short cycling.

Trying to heat 2 floors like this is never going to work well. The lower floor will be too hot and the upper too cold.

 

[Gunslinger99]

My understanding is that the OP wanted to only heat the lower garage.


I would think 200K would be OK if it was all one level. But with heating 2 levels the heater would heat the lower room too quickly and result in a lot of short cycling.

Trying to heat 2 floors like this is never going to work well. The lower floor will be too hot and the upper too cold.

Thanks. 200k seemed overkill to me but I wasn't sure. For some reason I thought the OP was trying to heat both levels.

This thread has me rethinking insulating the ceiling in my lower garge. It might be a good idea to let the heat below make its way upward and help heat the upper garage. I may try this first befor I buy a heater for the upper garge and see how it works.

I'm finding great info in this thread. Thanks

 

[ForceFed70]

Thanks. 200k seemed overkill to me but I wasn't sure. For some reason I thought the OP was trying to heat both levels.

This thread has me rethinking insulating the ceiling in my lower garge. It might be a good idea to let the heat below make its way upward and help heat the upper garage. I may try this first befor I buy a heater for the upper garge and see how it works.

I'm finding great info in this thread. Thanks

I like the idea of purposely letting the heat bleed into the upper garage. So long as the expectation is that the lower garage would be at the correct temperature while the upper will be "warmer than outside" instead of an expectation that the upper garage will be at the perfect temperature.

It would work well if the upper garage was used for only storage. Park vehicles, etc up there and use the lower garage for workspace (where you'd end up spending most of your time).

 

[bbarbulo]

i've read in sizing your heater (and my HVAC guy agreed) that you want to keep it reasonable. 40-50K BTU for a 2 car garage - too big and it won't give the heater a chance to reach operating temp before shutting off; meaning it does not run efficiently. 85K sounds about right for your situation.

I got a 50K for an insulated 2 car garage (about 18x22 roughly)

BTW, i love those garages w/ a lower and upper level!

 

[Gunslinger99]

i've read in sizing your heater (and my HVAC guy agreed) that you want to keep it reasonable. 40-50K BTU for a 2 car garage - too big and it won't give the heater a chance to reach operating temp before shutting off; meaning it does not run efficiently. 85K sounds about right for your situation.

I got a 50K for an insulated 2 car garage (about 18x22 roughly)

BTW, i love those garages w/ a lower and upper level!

Who's situation are you referring to for the 85k?