How long does a full propane cylinder fuel a single burner on Lo?

1 gallon of propane actually contains a little under 100,000 btu. You need to look at the rating plate on the burner and see how many btu it is rated at. Keep in mind that this number is the full capacity of the burner. If you turn the burner down, the btu output and fuel consumed will be less. uming for a minute you are talking about a regular BBQ tank, you have a little under 5 gallons. So that equates to about 450,000 btu's. Divide 450,000 by the btu rating and that is how many hours burning time you have on full heat. If you are throttling the burner down you're burn time probably wont double, but pretty close to it.