Here in upstate NY it gets pretty cold. My garage is uninsulated, and insulating is at the top of my "project" to-do lists. I have a 4000 W Infratech infrared heater (like they use in outdoor restaurants) mounted on the ceiling over my work area. Throw in a couple of 1000 W halogen work lights, two layers of thermals, and I changed the clutch in my car two years ago when it was 4 degrees. It was kind of like swimming in a very cold lake; hard getting in, but not bad once you were in
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Still gotta insulate. The problem is, when the weather is nice, who wants to work on the garage instead of in it?