Simply, the excellent design in tank top heaters!
Dura Heat TT-360 Tank Top Heater, 30,000 to 40,000 Btu, 1000 sq-ft Heating Area, Gasoline, Silver This Dura Heat tank top heater provides up to 40,000 Btu's of infrared heat in a 360 deg radius.. With variable heat output (30K/35K/40K), this versatile tank top heater is a great low cost solution for extra heat in many outdoor situations.