A/C Unit Size for 36 x 30 shop

[tonysellscars]

My 36 x 30 garage starts being built next week.

I am having the builder frame a hole for ac unit.

My question: What size unit does it need to be to cool this shop effectively?

I don't want to make a mistake and under cool...but also not over cool and waste money.

However, id rather be over cool than under!!

Thanks!

 

[tylernt]

"Frame a hole", as in, for a through-the-wall unit?

If so, you may want to have him frame a 4' wide hole so you can use a PTAC (the type used in motel/hotel rooms). PTACs are generally more efficient than a window/through-the-wall A/C, and have more features (such as "freeze protection" that keeps your shop at 40°F when not occupied in the winter). And, of course, most PTACs are reversible heat pumps, which makes heating 2/3 cheaper than pure resistive electric heat.

36'x30' is a big space, I'd go with a big unit, probably a 24K BTU/h or 2-ton. Don't forget insulation and attic ventilation! And a 240V outlet, most "big" A/C units are 240V.

Over-sizing the A/C will not cost you money. The thermostat will shut the unit off to keep the setpoint where you want it. What happens when you oversize is, the unit doesn't dehumidify properly. But, you have over 1,000 square feet so I don't think 24K BTU/h is excessive.

 

[Falcon67]

I'll say 24K in that space, depending. Not really enough info. Might be plenty with a 8' ceiling and not near enough with a 12'. If you have the budget, I'd look at mini-splits rather than a window unit. I can manage the heat in my shop (24x40x8', two rooms) with 17K BTU. That's a 10.5 in one room and a 6.5 in the other. It's a little on the light side, but it's what we had so the price was right. A couple of fans help distribute the air and I'm quite comfy.

FWIW - the tower at the drag strip has PTAC units. They are the absolute worst POS units I've ever seen. I don't know the brand, but they've spent big bucks over the years trying to keep those running without much success. Out of 4 units, at least one dies every summer.

 

[tylernt]

PTAC units. ... They are the absolute worst POS units ... at least one dies every summer.

What brand are they?

 

[Falcon67]

If I think of it, I'll look. I think the new owner has replaced the office unit (ground floor) with a mini already.

 

[Ohmthis]

We need more info. Type of building, what insulation in walls and ceiling, got any shade around, how cool do you want to keep it, budget, and I see that you are in Tennessee, it gets hot and humid there. Shoot a reply and we'd be glad to help.

 

[Milton Shaw]

Normally for a shop you get the biggest you can afford, that way you can turn it on and be cool enough in 30 minutes or so to work, same with heat. Same reason for when you open the doors the bigger one will catch up sooner. Now if the shop is heated/cooled 24/7/365 and the doors not opened then one sized right would be the correct choice. It depends on what and how you are using it to determine what you want. Mine for instance on heat I leave it set at 45 or so and then bump it up to 65 for working in there and it's comfortable in 15 minutes.

 

[Falcon67]

What brand are they?

Carrier. The new unit is a 24K Sanyo (IIRC) mini and it kicks ***. Cooling the first floor is about 400 sq ft, but it's a steel building with minimal insulation in a sea of asphalt. Both the W and N sides of the building catch the afternoon sun.