I'm working on my 53 3100 in the garage some over the winter. I have an Empire propane furnace (77K BTU) and was wondering if anyone else has any experience with propane wall hanging furnaces. How long should a 100 pund tank last?

The garage is a 3 car, with r-13 in the ceiling and r-11 in much of the walls.

I saw a 30K BTU model in the store that said it would go 72 hours on a tank. I'm sure that I wont get close to that.

any advice?