I had the opportunity to visit a local farmers tractor workshop yesterday. It was about 48 degrees and overcast with 20 mile winds. The front door of the shop was cracked open for ventilation. Inside the shop it was bright and warm, probably above 72. The interesting point is that it's not a typical shop. He built it from a double layer inflated greenhouse. He says the plastic lasts 7 or 8 years before it needs to be replaced. The free heat and light more than pays for the plastic replacement. He saves on property tax also.