Look at the mini split units - some are DIY
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Look at the mini split units - some are DIY
A window unit will go a lot farther than you might think. I have one in my shop but it's relatively small (24'x36'). You have to turn it on early in the day or in the evening to expect excellent results though, and it won't cool the areas far away from the unit. You need insulation too. A friend of mine in central TX has one in 40'x50' metal building. He bought the biggest window unit he could find. It's fairly well insulated and it actually stays fairly cool in there near the unit. (Low 80s on a 100° day). With a good fan it's not too bad.
My garage/shop is 28x32. I have block walls and small windows. I have I think 10 or 11K btu window unit. I measured ahead of time and removed the entire window and frame just leaving a surface of 2x8's around, stuck the air in good and made a plexiglass double pane fixed window above it. I set it at 70 when I'm out and it goes up to almost 75, when in there I set it low and it get's down to 68. Costs me less than $50 on the hottest month and I also do real paying work in there so it's worth it. I do have most of it insulated but half of what isn't insulated is underground.
Well I made some more changes to my shop. When I added a paint room I put four 4 ft. LED shop lights in the middle of the ceiling. It seemed nice and bright until I really tried to work in there and decided I need more light. I added eight more 4 ft LED shop lights, 2 on each wall.
I added an exhaust fan. I cut a hole in the walk in door and installed filters for incoming air.
I also got me an electric furnace. There is one vent in the tool room and two in the paint room. I also insulated the 16 ft. door separating the paint room from the rest of the shop. This morning outside temps were in the 20s, inside of shop was about 50 degrees. The furnace got it up to 72 degrees in less than 30 minutes.
You can't beat that. Sounds like you made a good choice on the furnace.