How Long Do Your Propane Tanks Last

On a weekend where the weather was in the teens at night, I had my furnace at 78-80 in my rig because I was storing temperature sensitive supplies for actors (stage makeup, facial prosthetics, etc... where freezing would completely destroy the items.) I managed to go through two 20# tanks and make a significant dent on a third. The main reason for the high usage (other than making sure the stored stuff was above freezing) was due to the lack of internal insulation coupled with single pane windows which caused heavy heat loss.

When the temperature is warmer, I can go a couple weeks without worrying about exchanging cylinders.