AC question

[Dave Aronson]

my "shop" is in my 3 car garage along with bikes and kids toys. Until recently it has not been too bad but lately it has been hitting triple digits and my shop is way too toasty to do anything in it. I've insulated the garage doors, insulated the attic above the garage and put in a small window AC unit (6000 btu). It is not awesome in there....

What solutions have people done for this? I don't think my wife will let me spring for a split level ductless system. I saw that they run about $4k.

[Bob Riefer]

Sounds to me like you've basically done the right things, (namely, insulating) but that you've chosen too small of a window unit. There are btu calculators online that will help you decide how big of a unit to purchase. If you watch craigs list you can score one for cheap. Or buy new. Keep the filter regularly cleaned, and you should be pretty comfortable.

edit: if you're in a very sunny area, a radiant reflective layer in your attic will bounce a bunch of heat out before it can penetrate your shop. But, if you used decent insulation (ballpark: R13 or better in the walls, R6 or better on garage door, R19 or better in ceiling [but preferably R30]), and upgrade your window AC unit, you should be in business.

[David Kumm]

I think my ductless ran closer to 3k. A little undersized is fine since you don't need full cooling. Removing the humidity helps a lot but dehumidifiers are useless so running the AC is fairly cost effective. I turn mine down an hour before I go in the garage, try not to put hot cars in and out, and only open the doors to move the cars. Training your wife to leave the vehicle out and close the door is the hard part. I actually oversized a little so it would cool a little faster and could be used less but it still runs on a 20 amp circuit. I consider it as important as a tool- and I live in Wisconsin. Dave

I checked my unit, 2 ton Fujitsu installed cost $2879 in July 2010. Again, I'm in WI but my garage is about 1900 sq ft with 10' ceilings and unit is more than adequate for hobby work.

[Joe Leigh]

There are a lot of factors that contribute to heat load but as a "general" rule of thumb figure approx 400 sq/ft per ton (12,000btu) of AC.
Based on an 8' ceiling height. Garage sizes vary but based on a 10' x 20' single garage, your garage may be, at a minimum, 600 sq/ft. That would require minimum 1-1/2 tons of cooling (18,000btu). Remember that's based on an 8' ceiling which few garages have. From there you have to account for additional lighting and internal heat gain from equipment and machinery. I would say 2 tons minimum (24,000btu).

[Lee Schierer]

As others have stated your AC is probably undersized for the area you want to cool. I find that a large industrial type ceiling fan installed directly over where I normally work will cool you off quite a bit. They are cheaper than another AC unit and would make the room more bearable with your existing AC.

[Don McManus]

In my previous garage I had pretty good luck with a 2ton(24000btu) window unit in a 600sqft garage(sloped ceilings 7-14ft tall) with r11 walls, and r19 ceiling, 5 windows and 2 wooden garage doors. Helped a lot to seal gaps around the garage doors. This was detached garage, and the 2ton could keep up with all but the very hottest Houston days.

My new garage came with a 1.5 ton split. For a 420sqft space with 9ft ceilings, it is complete overkill. Cools the palce down in minutes, plus garage doesn't get that hot because its attached(today is 103 outside, 87 inside garage at 4:30pm, air has been off). Since it was already insulated by builder, all i did was fill in the bare metal garage door panels with polyiso board(more rvalue/inch than styrofoam). The panels bay's were 1-1/4" deep, so I used a 3/4" layer and 1/2" layer, for a snug fit.

just some points of reference. hope it helps

Don

Also, a fan helped me a lot more in 10% Vegas humidity. It does very little in Houston's 99% humidity, so I use A/C for dehumidification as much as cooling the temps down.

Edit: also Having only one unit centered in my 3car space created hot and cold spots. I can remember saying that if I was to do it again, I'd have gotten 2 smaller units to even things out. You might be on the right track with one 6k unit, and one 12-18k, depending on your insulation and sun exposure.

[Kevin W Johnson]

As others have stated your AC is probably undersized for the area you want to cool. I find that a large industrial type ceiling fan installed directly over where I normally work will cool you off quite a bit. They are cheaper than another AC unit and would make the room more bearable with your existing AC.

Except for potentially turning the garage "shop" into a big dust bowl....

[Scott T Smith]

Dave, one thing to consider is to simply add a second window type ac unit in a different part of the garage (using a much larger unit). If you leave the current unit running for most of the time set at 80 degrees or thereabouts (or start it a few hours before you want to work), it should keep the humidity fairly low in the garage shop, which is good for wood acclimization. a 6K BTU unit does not cost that much to run either. Then turn on the second unit an hour or so before you want to work in the shop. Some fans to circulate the air throughout the garage would be beneficial too.

[Lee Schierer]

Except for potentially turning the garage "shop" into a big dust bowl....

That's what DC systems are designed to prevent.

[Dave Aronson]

Thanks for the feedback. In regard to radiant barrier, my roof already has that :-) my ceilings in my garage are 12' so I sounds like I need to be on the lookout for a 18k or bigger unit. I only have one window so only a single unit will work for me.

[Don Jarvie]

You want to add a ceiling fan or two to circulate the air. That plus a bigger unit should help.

I have a fan in my 20x20 shop and its great. Its one of the best things I put in the shop. Moves the air enough so its not stiffling. I have no AC since it doesn't get too hot up here in Boston too often.

[David Hostetler]

Your AC is radically undersized for the space you are trying to cool. I use a 13.5K BTU unit in an 18x20 garage insulated similar to yours, and it struggles to keep up the the temp hits 100 outside. I need a LOT more insulation!

Another thing that helps, a LOT is to keep the air moving in the shop. I use the ambient air filter while I am in there, it is very useful for keeping some areas from being oven hot, and some areas from being freezer cold... I must admit though, the most comfortable place to be is at the table saw or drill press as those machines are closest to the output of the A/C....

[Dave Aronson]

I'll start adding fans, and looking for an AC unit. most of the ones I see on craigslist look pretty sad so I think I'll be getting a new one.

[Kevin W Johnson]

That's what DC systems are designed to prevent.

That's why i said potentially, because he doesn't mention having a DC system and no one thought to ask before recommending fans.