Clean oil fired unit heaters are designed to operate with No. 1 and No. 2 clean fuel oil. Completely factory assembled, pre-wired, fire tested, and UL listed to utilize fuel oil grade No. 1 or No. 2. Oil-fired unit heaters offer an efficient and reliable way of heating a space, particularly in regions where supplies of other fuels, such as natural gas, may be unavailable, undependable, or interruptible.