How Long Does a Propane Tank Last? Grill, Heater & Furnace Chart

A standard 20 lb grill tank lasts about 12 hours on a 3-burner grill running flat out, and commonly 15 to 20 hours of real cooking. Bigger tanks and smaller appliances stretch that a long way. The answer always comes from the same sum: the energy in the tank divided by how fast the appliance burns it.

The formula

Propane is sold by weight (cylinders) or by the gallon (bulk tanks), but appliances are rated in BTU per hour. One gallon of propane holds about 91,500 BTU and weighs about 4.24 lb, so one pound holds about 21,600 BTU.

A 20 lb tank holds about 4.72 gallons, which is 431,880 BTU. On a 36,000 BTU/hr grill, that is 431,880 ÷ 36,000 = 12 hours at full power. The propane tank runtime calculator does this for any tank and appliance, and lets you set the average power and your hours per day.

Propane in common tanks

Cylinders are labeled by the weight of propane when full. Bulk tanks are labeled by water capacity and are filled to no more than 80%, so the usable propane is smaller than the label.

How long will it last? (hours at full power)

These are the runtimes with each appliance burning at its full rating the entire time. Real use is lower, so a tank lasts longer than the numbers below. A thermostat-controlled furnace or heater cycles on and off, and a grill is often at 50 to 70% power.

For a whole house, the bulk tank has to supply the furnace, water heater, range and dryer through the cold months, which is why most homes with propane heating use a 250 or 500 gallon tank and arrange regular deliveries.

How to tell how much is left

• Weigh it. The "tare weight" (TW) is stamped on the collar of the cylinder. Subtract it from the total weight and what remains is propane. A full 20 lb cylinder weighs about 37 lb in total.
• Use a gauge. A dial or a stick-on gauge between the tank and the regulator, or a smart monitor, shows the level.
• Warm water trick. Pour warm water down the side. The tank feels cool to the touch up to the liquid level. It is rough, but it works in a pinch.
• Bulk tanks have a built-in float gauge, in percent. Order a refill before it reaches 20 to 30%.

What makes a tank run out sooner

• Cold weather. Propane vaporizes from the surface of the liquid, and a small tank in the cold cannot do it fast enough for large loads, so heaters and generators may starve.
• Leaks and poor regulators. A slow leak wastes fuel and is dangerous. Test connections with soapy water.
• Running burners on high. Burners at full power use far more than at low. Cooking at medium saves a lot.
• Opening the lid. Heat loss makes a grill burn more fuel to hold the temperature.

Safety

• Never store or use a propane cylinder indoors, in a garage, a basement or a car. Keep it upright and secured.
• Never fill a tank above 80%. The empty space is needed for expansion when it warms. Cylinders are filled by weight at a refill station, which handles this for you.
• If you smell gas (rotten egg odor), turn off the valve, get away, avoid any flame or spark, and call the gas company or fire department.
• Check hoses and fittings each season for cracks, and replace cylinders that are rusted, dented or past their recertification date.