OBSOLETE - This is the 50W oil preheater that was used in the 85 HS, 90 HS and 90-HPB-AIR Clean Burn waste oil furnaces. It has been made obsolete. The 300W replacement heater (33096) is to be used in the air side of the block and heat the entire block. Then you can plug off the oil side or leave the heater in and cut the wires.