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Removed AC’ing of garage…now I understand why it was there to begin with…

user-5167482 | Posted in General Questions on

Hello – I put 3 months of effort into refurbishing the garage. i own a 2 story house where the the ceiling of the garage is the floor of the 2d story – that is, there are two bedrooms and a hallway directly above the garage.

Although there were a myriad of issues in the garage space, it was noted on the inspection report (I bought the house 2 years ago) that there were air intakes in the garage and this is obviously a bad idea (car exhaust, other fumes, etc). I also discovered that there were ducts leading into the garage AC’ing the garage. Odd, since the garage leaks like a sieve.

It was very, very poorly done work rough in work. So I tore the drywall off the ceiling and a portion of the walls. Did a lot of air sealing and duct re-work. Put pink insulation foam into the floor joists and then two 1/2″ polyisocyanurate. Followed up with 1/2″ lite sheetrock. (FYI, followed this GBA detai – https://www.greenbuildingadvisor.com/cad/detail/air-barrier-garage-band-joist-1-rigid-insulation-1×3-wood-furring)

So, I thought I had done good and from an air leakage, energy efficiency point of view I did. I discovered this winter though (I live in Virginia, right outside DC) that having the garage AC’ed kept the living areas above the garage much easier to heat. The upstairs, as a result, has been freezing! I guessed incorrectly that having done a great job air sealing and insulating and adding the polyiso, which wasn’t installed before, would have created a good enough thermal barrier between the now un-aC’ed garage and the living areas above. The total R-value of the ceiling is at least R-40.

So…Looks like I have some more work to do. I plan on ripping the drywall off the walls in the garage to correct many rough-in hacks and do some remodeling too. I was thinking I could install a separate AC system in the garage to at least keep it within 10 degrees of the internal house temperature. I was thinking a wall unit could work…or something similar?

I recall reading here before that it’s not as simply as I am thnking. Any advice, thoughts on this from the experts? Thanks, much appreciated!

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Replies

  1. charlie_sullivan | | #1

    If you've got R-40 between the garage and the space above, and no air leaks there, the temperature of the garage won't affect the temperature of the rooms above much at all. I would look for other heat losses in those rooms, and look at the duct system--is it really delivering heat to those rooms now?

  2. Andrew_C | | #2

    I think you may get better advice if you clarify what you are trying to do. You say "AC", which normally means air conditioning to cool and dehumidify. But you are talking about heating the space in the winter. I suspect that when summer comes around, you'll want air conditioning for cooling as well. Maybe it's just me that's confused.

    If you want completely separate heating and cooling systems for garage, versus the rest of the house, you might consider a mini-split, ductless or otherwise. There are a lot of articles on this website on mini-splits.

    If you're thinking that you don't want any duct work connecting the house and the garage, I'd say that's wise.

  3. user-5167482 | | #3

    Answering Mr. Sullivan - yes, the rooms above the garage are being heated by the A/C system. I think I wlll pick up an IR sensor to see where I am losing energy or leaking air elsewhere. The exterior of the house is remarkably poorly insulated. Another project for another day I guess.

    Answering Mr. Andrew C - I am using A/C in the general sense where it is used for heating or cooling. I looked into the mini-split system; I think it is a viable option. I should have performed some careful measurements of the temperature difference between the garage and rooms above before I did the re-work. That way I could have some data to back up my hypothesis. Oops. I suppose I can rent a propane heating machine and heat the garage and then perform measurements in temperature differences between the upstairs when the garage is heated and when it is not heated. Actually, that's a good idea. I'll do that.

  4. charlie_sullivan | | #4

    I'd go with electric space heaters for the temporary garage heat, so you aren't getting the fumes and moisture that a propane heater generates into your garage. And if it's only short-term, the electric bill isn't a big deal.

    I agree that it's a shame A/C has come to mean air cooling and dehumidifying, leaving out heating and air quality. An alternative catchall is HVAC (heating, ventilating and air conditioning), which works as long as you don't confuse it with high-voltage alternating current.

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