Guys no need to freeze in the winter, cheap heat buy a MR. Heater radiant heater that bolts on the top of a propane gas grill bottle $50.00 it makes things comfy.
If you want the shop to heat fast use their 60,000 btu propane torpeto heater which works on the same gas grill bottle. $108 when I bought it from Lowes on sale.
Just leave a crack in a door / window for some ventalitation.
It has been in the -0 degree numbers this winter, and I can keep my old shack at 80 degrees any time I want.
Propane runs me about 17 bucks every 2 weeks, but it is worth it to play with the old car for a couple of hours every night.