While the flame provided by burning the liquid bio-ethanol fuel for fireplaces is decorative and beautiful, it also is efficient in providing heat. Due to the ventless nature of the fireplaces themselves, no heat is lost up the flue or vent. Depending upon the size of the fireplace and opening of the fuel tray, it can produce anywhere from 1,500 to 70,000 BTUs / hour of heating energy. Just to give you an idea, 5000 BTU's is enough to warm up a 450 sq. ft. room.