For Maximum Operation Due to the pressure in the Propane tanks, many of our heaters require a 100 lb. tank or larger to operate. Propane tanks that are less than 100 lbs. do not have much pressure. The propane ends up freezing in the pipes, which ruins the heater and Voids the Warranty. We recommend that all of our customers use a 100 lb. tank or larger unless the heater description tells you otherwise. Rule of Thumb for heater tank sizing is:75,000 BTU heater needs a minimum of one 100 lb. tank. 150,000 BTU heater needs two tanks manifold together and so on.