My shop has 10'x10' doors, 3 of them. They are wood and very heavy, so I had them all replaced with insulated doors. They are very light and much tighter in the seals. Also replaced the side door with steel insulated door. Then replaced the 3 windows which were original to the shop from 1975. They were plexiglass pull downs which were replaced with double insulated glass windows. I put a new heater in 2 years ago and had it all checked out and cleaned when the guy I use did the house heater. I am ready to go and be much warmer in the shop.