I use LP a 200,000 unit forced air H.E,Before anyone say anything it is a counter flow. my shop is just under 2000 SQ.Ft. with 9' ceilings, I turn the thermostate down all the way at night and never over 65 during the day..This ones been out there about 2 years the first one lasted 12 years here and 3 years in chicago (moved it here ) I can't complain, We heat the house with wood...Not free still have to spilt and stack and carry in.. Not going to get kero. by the 5 gal pal? But thanks for the info.