Well I guess I told a fib as my furnace is always plugged in and set to go on at 50 degrees. It is the same furnace that we have in the house and burns oil. I used R-38 in the ceiling and R-19 in the walls so the 6" thick 24' X 36' slab helps in keeping things stable as the floor temp stays in the 50 to 60 degree range all year long. In a normal year I use about 150 to 200 gallons of oil in the shop. I turn up the thermostat in the shop to 65 degrees when I go in and that heats the shop to about 70 degrees and very seldom does it come back on while I'm in there. When we moved out here heating oil was $.53 a gallon now my friend (who is a woodturner) drives the oil truck and I leave it up to him to fill them up each year when he thinks the price is at its lowest.