To work out how many hours burn in an LPG gas bottle, divide the ... A 23,700 BTU heater will last 3.86 hours (91,502 ÷ 23,700 = 3.86) ... For example, if a burner uses 22,875 BTU per hour, it will last 4 hours on a ... the consumption specifications for the lower settings, so you can still do your calculations.