Window A/C for HOT shop .. help

[Floyd Cox]

I am thinking about installing a 22,000 BTU Window A/C unit in my metal building it has sprayed foam insulation on the walls and ceiling which helped some but still very miserable during the summer.
The size of the shop is 24x30 with a 12’ high open ceiling, do you think a 22000 BTU window unit will bring the temperature down to maybe 80 – 85 degrees when it’s in the high 90’s outside?

[Alan Bienlein]

I have a 24 x 24 metal building for my shop that's 12' at the peak with 9' high walls. I insulated the walls with the 3/4" thick foam insulation from Home depot that has foil on one side and white plastic on the other. For the ceiling I went with 1-1/2" thick duct board. I can get mine down to 70 degrees with the 25,000 btu window unit I installed in mine.
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[Thomas Canfield]

I can't speak to the Btu needed, but you might want to consider some oscillating fans to help get some air flow and circulate the air. I try to get some circular air motion going in my shop with air filter, oscillating fan mounted on ceiling, and the output of my little window air conditioner wall mounted 6' above floor to get air movement above tools, etc.

[Floyd Cox]

Alan, how did you mount the the insulation to the metal?


I have a 24 x 24 metal building for my shop that's 12' at the peak with 9' high walls. I insulated the walls with the 3/4" thick foam insulation from Home depot that has foil on one side and white plastic on the other. For the ceiling I went with 1-1/2" thick duct board. I can get mine down to 70 degrees with the 25,000 btu window unit I installed in mine.
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[Mike Wilkins]

Floyd I have similar insulation on the underside of my shop roof. I just used roofing nails to attach the panels to the rafters. Its just foam with foil-like material on one side and plastic sheet on the other.

[Jim Andrew]

Do you have a flat ceiling, or just the bottom of the sheet metal sprayed? An attic seems to help a lot in steel buildings to keep the working area from building up heat during summer. Just a suspended ceiling can do wonders. The area above the ceiling does need to be vented if at all possible.

[Rob Damon]

I have a 24'x50'x 10' ceilings,but with wood framing. A 24,000 btu window can keep the shop at 68 deg year round with summer temperatures hitting 100 deg. if I needed it. I normal try and keep it at 70 degrees in the summer and 65 degrees in the winter. The key is insulation and more insulation and draft stopping. I have R-13 in walls and R-38 at underside of roof. So a unit that size with proper insulation is more than capable handling a space that size.

[Kent Adams]

I would think 22k BTU is plenty to cool that space. My shop, although made of wood, is cooled by an 11k BTU window unit and I can get it down to 70 degrees when its in the high 90's outside. I decided to go with a "hot roof" so that meant I had to insulate and seal very well to prevent condensation from developing on the insulation. I would think the foam spray would insulate from leakage very well. As someone else said, one of your challenges will be your ceiling height. Ideally, I would do what Alan did and put up a reflective radiant barrier up. This was very helpful in my shop, I have it on all the walls along with traditional insulation r-13 in the walls. I dropped my ceiling a bit and added R-38 rolled insulation on top. If you could drop your ceiling a bit, add an air filtration system, such as a Jet 1000b, you should have no problem keeping that shop in the 70's during the hottest day of the year. Disclaimer: Metal buildings may present additional challenges I don't know about. My micro shop is 12x24. Good luck and happy woodworking.

[Joe Bradshaw]

Floyd, my shop is 24x36 with 9 ft ceilings. I went overboard with insulation when I built it, including under the slab. I use an 18,000 BTU unit for heating and cooling. It works well for me.
Joe

[Matt Meiser]

A 24,000 BTU unit worked well for me in a 30x32x12 shop with R19 walls and crazy amount of blown cellulose in the ceiling, but also a huge 12x12 roll up door.

[Floyd Cox]

I just wanted to thank all of you for the advice you have taken the time to give.