Air conditioning survey....

[Marc Spagnuolo]

Hello everyone. I am looking to install a window AC unit in my garage. I have about 1250 sq. feet and 14ft ceilings. I know that is a heck of alot of air to cool (especially in the desert), but I am really just looking to make the temp a little more reasonable. Sweat drips will raise the grain

So I am curious: if you have an AC unit in your garage/shop, what BTU rating do you have and how big is your shop? The online calculators tell me I should be going for 23-25k BTUs. I found a decent one at Sears that is 28k and I think that might be the way to go. Thanks ahead of time.

Marc

[Randy Meijer]

Here in Texas the rule of thumb for a residence is 1 ton of A/C for about 450-500 sq. ft. With a ton being about 12000 btu, you are looking at 33,000 BTU and that makes no allowance for the high ceilings and the big(and presumedly uninsulated) garage doors. And you didn't mention whether your garage was insulated and if so to what R factor. Sounds to me like you might be undergunned with a 2 ton unit(24000 BTU) but I guess it also depends on whether you want the garage top be 85° or 65°. Another factor would the type of tools running as they would contribute to the heat load. I'm thinking that you need to be talking to an A/C pro. This kind of calculation is a little tricky and it is easy to get it wrong!!

Do you spend most of your time in one part of the shop...........maybe you could block off one section of the shop with heavy plastic sheets and only A/C part of the 1250 sf. Putting in some sort of a false ceiling would help a bunch too.......even if it were nothing more than stapling 8 mil poly to the joists(?).


Another consideration.....a lot of big A/C units need 220V. Do you have that available or will you need to do some wiring??

[Jimmy Walker]

Randy has some very good points Marc.

I only have 336 sf and I have a 10k unit. Does a great job. RH is the big deal here. Don't you have low RH in the desert?

Seems some sorta swamp cooler would work better for you, huh? Or would it introduce to much RH?

Your cost per KWH on electric rates is pretty high too, I think. Only cost me about $35 a month in summer to run my shop. Got separate meter for it.

I know it's worth for me. Couldn't be out there if I didn't have it.

Just 2 cents worth.

[Dennis Peacock]

Marc,

Good question to be asking this time of year.
1 Ton of A/C Cooling is equal to 12,000 BTU
Depending on where you live is different "rules of thumb" for figuring what you need. Around here is 600 Sq Ft Per 1 ton of A/C.
My shop is 1,800 Sq Ft and during the HOT part of the summer I section off one bay and that reduces me to 1,200 Sq FT. and I can and do cool that to somwhere between 74º F and 81º F.
I am using two window units. One 6K BTU and one 12K BTU for a total of 18K BTU of cooling. This done fine for me and I can leave the small unit running all the time and then turn on the larger unit when I get home from work and let it cool some before I actually get in the shop.

Of course, to do it all up right, you'd have to take into accout the heat load, ceiling height, amount of insulation you have, windows, doors, lighting heat load, machine heat load....blah....blah....blah......

In short, I'd say put you in two 12K BTU units and enjoy the cooler temps in the shop. When I go in my shop from the outside in the heat, it's almost chilling. And I'm a hard person to cool in the summer months.

[Ron Jones near Indy]

My shop is 576 sq. ft. with 8 foot ceilings and very well insulated. It is no problem to cool it with a 6000 BTU window unit. We had temps in the 90's with high humidity in the last 2 weeks--74 degrees in the shop. Had I turned it down, I think I could of gotten it below 70. My point is insulate, insulate and insulate some more.

[John Lucas]

The key difference is insulation. I amin RI and ahve a two car garage shop that is insulated and the big doors are self made and have insulation throughout. Small Dawg Heater works well. 12000 btu window unit keeps it at 72 no matter what the outside is. But insulation is key.

[Ed Blough]

I have a two car garage 450 sq ft with three exterior walls and back wall attached to the house all 8 ft construction. Construction is concrete block with an 18 foot aluminum door. The attic has no insulation save the junk kept up there. I cool it with an 10,000 Btu Maytag window unit. In Florida we have an abundance of humidity and heat. However the window unit will pull the temperature down to 72 -75 on the hottest of days. I will say that if the garage is really warm before I turn the air on it will take a while. Therefore I try to turn it on early in the morning on the days I'm going to work in there.

[Ellen Benkin]

I would suggest adding both insulation and an attic/roof vent fan to help with the cooling.

[Matt Meiser]

I have a 24K BTU model cooling 30x32x12. I have an insulated overhead door, double pane windows, R19 in the walls and about 18" of cellulose in the ceiling. Works great and only runs about 1/2 time on the hottest days.

[Silas Smith]

I have a 12,000 BTU window unit cooling a 20X24 garage. I share two walls and a ceiling with the house and I have put some makeshift insulation on the garage doors. I basically open the garage door enough to slide the window unit underneath it and then put some styrofoam in to block out the gaps. I spend about 5 min setting everything up but it is well worth it in Houston. I had a friend who said living in Houston in the summer is like living inside somone's mouth.

[Alan Tolchinsky]

I have a 12,000 BTU window unit cooling a 20X24 garage. I share two walls and a ceiling with the house and I have put some makeshift insulation on the garage doors. I basically open the garage door enough to slide the window unit underneath it and then put some styrofoam in to block out the gaps. I spend about 5 min setting everything up but it is well worth it in Houston. I had a friend who said living in Houston in the summer is like living inside somone's mouth.

How do you block out the top of the door? On my roll up door when I open it 6 inches, there's a big gap at the top. Just wondering but ain't a/c a great invention!

[Brian Austin]

I also live in Phoenix and have two setups. My old shop, in a 20x20 garage, was cooled with a 18K BTU a/c unit mounted in a block wall. The garage is on the south side of the house. There was lousy insulation above the garage and two of the walls with connected to the house. The a/c unit seemed to keep up just fine, though. Open the door to move something and it would take a while to recover. I also used an oscillating fan to keep the air circulating, which seemed to help.

In my newer dedicated shop on the side of the house, I have the same 18K BTU a/c unit (different unit, same model) cooling a 14x24 space with no ceiling (straight to the roof). The building has R-13 fiberglass insulation and 7/16" exterior siding for walls. The upper rafter area is open (mainly due to my desire to have a larger 'feel' to the place). I've installed some reflective barrier right under the roof sheathing on the inside. It seems to have an impact, although I really have no hard numbers to prove it. The a/c is on everyday since the dog has a 10x10 kennel on the outside the shop with a 4x4 interior space to escape the heat and rain (when it happens). With the thermostat set at 85, it's comfortable in the shop in the heat of the day (I drop it to 82 when I'm working, though). I need to add another dog door, however, since she chewed up the last one and it's just an opening at the moment. I'm building my own since (a) they want WAY too much for those replacements and (b) she'll just chew that one up as well. I'm thinking 1/4" plywood with steel banding should do the trick.

[Jim Tobias]

I have the Sears 23K BTU window unit and it cools my shop (32x32 with 16' ceiling). I usually set it on about 74 and it does fine.


Jim