Calculating A/C size for new garage

[mastiff0]

First post here guys. Love the site.

I'm closing on a house that has a 31' x 32' detached garage. Its a blank slate, unfinished walls and open attic and such, and I plan to beef up the electrical system, insulate, and cool the sucker. I have a lot of questions that I hope this forum can help me with, but the first question is about the A/C system.

I've seen simple tables that say for the size of my garage (1000square feet), I need an 18000BTU unit. However, I know that these numbers are designed for rooms in the house, not in the garage. I'm going to insulate the walls, roof, and garage doors, but I'm going to have taller ceilings (not closing in the attic) and know that I will get some heat from the big garage doors.

On the other hand, I'm not expecting to have the garage at 75 degrees. I'm just wanting to get it tolerable and to remove some of the humidity.

So, does 18000BTU sound right for a 31x32x10 garage, or have people learned from experience that you will need a little more/less cooling? Thanks guys.

 

[Trackrocket]

I will be tuned into this thread indeed as I have just built a 30 x 32 "shell" garage with 2nd floor storage area (attic) and plan on insulating, installing drywall and possibly an HVAC setup.

 

[mastiff0]

Well, I spoke to a local HVAC guy to see his prices on mini-split units, and I asked him about size recommendations. He first told me that I would need 2tons (24K BTU).

I then explained that this would not be a "man cave" but a garage, which means that I planned on keeping the room fairly hot during the day, and even when I was using the garage, I would not try to cool it down to house-like temperatures. In Texas this means keeping it at 85F during the day and letting it come on to knock out the humidity, and then get it in the 75-80F range when I'm actually using it in the evenings. The HVAC guy said that an 18K BTU system could be used for that, and a 24K BTU system would only be needed if you were trying to maintain a 75F temperature peak day temps.

I also have a friend with a 3 car dettached (600ft2) that uses a 10K unit in the manner I'm planning. So the info from the HVAC guy and the friend have me feeling confident that a 18K BTU system will work.

 

[osu69]

I have 4 tons of AC and 90,000 BTU's of propane heat in my 28' X 48' garage with 12'3" ceilings. The four garage doors are about R-5, the walls have R-13, and the ceiling has R-38.

Located in GA with high heat and humidity. Cool down is fast; I like to work at about 75° in the summer and about 70° in the winter. Hot vehicles aren't really a problem with the extra AC capacity.

I probably could have gotten by with less capacity but I really like the quick cool down and fast heat up.

 

[CUSTOMMANCAVES.COM]

I have 3.5 tons (42k BTU's) for about 1000 s/f. Concrete block filled walls and poured concrete ceiling. Bumped that up from 2 tons (24k BTU's) as the 2 ton unit ran all the time trying to keep up. I may go to 4 tons (48k BTU's) in the future as the 3.5 ton unit still struggles.

Originally, I had one of those 18k BTU portable A/C units and that just didn't do it.

Your location is important. Heat/humidity in one location does not compare to another. I am in SoFLA. I keep my t-stat @ 78F.

 

[DavidTK]

2 tons won't cut it. I live in Texas and have 3 tons on my 1,200 square foot attached garage, so half of the garage isn't exposed to the sun. It's enough to get the garage comfortable for working, but in the late afternoon the garage gets to 90 degrees. It'll take an least an hour to get it into the low 80's. That's still pretty comfortable because at that point a lot of the humidity has been pulled out. I can get it below 80 in those conditions but it takes a while.

For you, I think the 2 ton will certainly help, but the unit will be running all the time. I would go 3-4 tons. I know you said you just want it tolerable, but man I can't describe how nice it is to work in a COOL environment when it's 90+ degrees outside.

 

[thomask]

"So, does 18000BTU sound right for a 31x32x10 garage, or have people learned from experience that you will need a little more/less cooling? Thanks guys."

I would think if the price difference is not that big you will be happier in the long haul with a bigger unit.

BTW Did you get a bid on different size units?