With this board installed in your furnace, the fan will no longer run all night blowing cold air. Board knows when the propane has run out or if the furnace did not light, and shuts the fan off one minute after the third try. It has the same great design features as the other Universal Ignitor Boards, but with an added fan control relay. For RV furnaces only. Fan 50 Plus works in furnaces with Suburban's and Hydro Flame's fan control feature, and can also be used to implement the fan control feature in most 12V DC DSI furnaces. Not recommended for use in the Duo-Therm 900 series furnaces where the thermostat is in the ground circuit. 3-1/4" x 4-1/4".