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Propane Heater Runtime & Cost Calculator

Find how many hours a 1-lb cylinder or a 20-lb, 30-lb, 40-lb or 100-lb tank runs your portable propane heater, what each hour costs, and whether the tank can keep up in cold weather.

Portable Propane Heater Runtime

Use the rating for the setting you actually run; it's on the heater's label.
A full 20-lb tank weighs about 37 lb; the empty weight (tare, "TW") is stamped on the collar.
A 20-lb tank holds about 4.7 gallons. Exchange cages often fill tanks to 15 lb instead of 20.

Your Propane Heater

Propane holds about 91,500 BTU per gallon at 4.24 lb per gallon, so about 21,600 BTU per pound; a 1-lb disposable cylinder holds 16.4 oz. Runtime assumes the heater burns at its rated input the whole time. Cold-weather limits for 20–100 lb tanks use a 100-lb cylinder vaporization chart at half full, scaled down by weight (a conservative estimate).

Runtime by Tank and Setting

Setting1-lb cylinder20-lb tank40-lb tank100-lb
4,000 BTU/hr5.5 hrs108 hrs216 hrs540 hrs
9,000 BTU/hr2.5 hrs48 hrs96 hrs240 hrs
18,000 BTU/hr1.2 hrs24 hrs48 hrs120 hrs
30,000 BTU/hr—14 hrs29 hrs72 hrs
60,000 BTU/hr—7 hrs14 hrs36 hrs

Full tanks, burning at the rated setting. Manufacturer figures line up: Mr. Heater lists its 4,000/9,000 BTU Buddy at about 6 hours on low and 3 hours on high per 1-lb cylinder, and its Big Buddy at up to 11 hours on two cylinders. The math gives 5.5, 2.5 and 11 hours, a little shorter because real heaters often burn slightly under their rating.

1-lb Cylinders Cost About Six Times More

Disposable cylinders are convenient, but you pay for it. At $6 a cylinder, a heater on 9,000 BTU costs about $2.40 an hour. The same heat from a 20-lb tank refilled at $4 a gallon costs about 39¢ an hour. Run it 8 hours a day for a week of camping, ice fishing or an outage and that's about $137 in cylinders versus $22 in refills. An adapter hose and filter that connect the heater to a 20-lb tank usually pay for themselves in the first weekend; follow the heater maker's instructions, since some models require their own hose and filter kit.

A 1,500-watt electric space heater puts out about 5,100 BTU an hour for about 27¢ at 18¢ per kWh, roughly 48¢ for the same 9,000 BTU. That makes refilled propane a little cheaper than plug-in electric heat, and 1-lb cylinders five times more expensive.

Cold Weather: When the Tank Can't Keep Up

Propane leaves the tank as vapor, and the liquid has to boil to make it. That takes heat from the air around the tank, so a small tank in the cold can't supply a big heater. A half-full 20-lb tank at 0°F can boil off only about 13,000 BTU an hour by our conservative estimate — less than an 18,000 BTU heater on high. The flame shrinks and the tank frosts. At 20°F the same tank manages about 19,000 BTU, and above freezing it's rarely a problem for portable heaters. Disposable 1-lb cylinders are the first to struggle in the cold. Moving to a bigger tank, keeping it out of the wind and off frozen ground, or running on a lower setting fixes most cold-weather fading.

Indoor Safety

  • Only use heaters marked indoor-safe inside tents, cabins, ice shanties or homes. Those have an oxygen depletion sensor (ODS) and tip-over shutoff. Tank-top and forced-air heaters are for outdoors or well-ventilated work areas.
  • Follow the ventilation the manual calls for and use a battery carbon monoxide alarm. Unvented heaters put all their exhaust and water vapor into the space.
  • Mind the altitude limit. Mr. Heater's indoor-safe Buddy models list a maximum of 7,000 feet, where the oxygen sensor can shut the heater off early.
  • Keep the tank outside the living space when you can and never store spare cylinders next to the heater.

For keeping a whole house warm through an outage, see how fast a house cools without power and the generator propane runtime calculator.

Related Calculators

Related Guides

Quick Facts

  • 1-lb cylinder: ~22,000 BTU
  • 20-lb tank: ~4.7 gal, 430,000 BTU
  • 9,000 BTU on a 20-lb tank: ~48 hours
  • 1-lb cylinders vs refills: ~6× the cost

Glossary

Frequently Asked Questions

How long will a 20 lb propane tank last on a heater?

A full 20-lb tank holds about 430,000 BTU. That runs a heater at 4,000 BTU an hour for about 108 hours, 9,000 BTU for about 48 hours, 18,000 BTU for about 24 hours, and a 30,000 BTU tank-top heater for about 14 hours. Exchange tanks filled to 15 lb last about a quarter less.

How long does a 1 lb propane cylinder last in a Buddy heater?

About 5 to 6 hours on the 4,000 BTU low setting and about 2.5 to 3 hours on the 9,000 BTU high setting. A 1-lb cylinder holds 16.4 ounces of propane, roughly 22,000 BTU. A heater with two cylinders on low runs about 11 hours.

Is it cheaper to use 1 lb propane cylinders or a 20 lb tank?

A 20-lb tank is far cheaper. At $6 per 1-lb cylinder, heat costs about $2.40 an hour at 9,000 BTU; from a 20-lb tank refilled at $4 a gallon it costs about 39¢. A hose and filter kit to run the heater from a 20-lb tank usually pays for itself within a weekend of use.

Is a propane heater cheaper than an electric space heater?

With refilled tanks, slightly. Heat from propane at $4 a gallon costs about $4.37 per 100,000 BTU, versus about $5.28 from electricity at 18¢ per kWh. With 1-lb disposable cylinders, propane heat costs about five times more than electric.

Why does my propane heater lose heat in cold weather?

The tank can't boil propane fast enough. Liquid propane needs heat from the surrounding air to turn into vapor, and a small or half-empty tank in freezing weather can fall short of what a high setting needs. Use a larger tank, shelter it from wind and frozen ground, or turn the heater down.