I run both a small woodstove and a 75K BTU sealed combustion chamber propane unit. I keep the thermostat on the propane unit at 45 degrees and fire up the woodstove when I go out to the shop each morning. We've been having a week or so of temps in the minus teens to minus 20's so the temp differential between outside and inside is quite large. Shop size is 30x30. Log walls and I insulated the attic to R-40.