Mr. Heater Big Buddy Portable Propane Heater 18000 BTU F274800. The latest evolution in powerful and portable Heat is here with the Mr. Heater Big Buddy Portable Propane Heater. Blasting 18,000 BTU's the Big Buddy Propane Heater will warm up the coldest spots. Designed for use while camping, in cabins, during tailgate parties, workshop, and in emergencies the Big Buddy Heater provides awesome heating. Let the heat wave begin with this portable heater powered by magical propane power.