How Long Does a Patio Heater Propane Tank Last?

A patio heater propane tank lasts about 8 to 11 hours on high for most full-size heaters, and far longer on a lower setting.

The exact number comes from simple division: the energy in the tank divided by how much fuel the heater burns per hour. A heater’s BTU (British thermal unit) rating gives you that hourly burn, so two heaters on the same tank can run for very different stretches.

WestAir provides propane services across California and Arizona.

How Much Propane Does a Patio Heater Use?

A patio heater burns between about half a pound and 2.3 pounds of propane per hour on high, with tabletop models at the low end and freestanding heaters at the top.

The BTU rating on the heater’s label is its hourly fuel draw at full output.

A gallon of propane holds about 91,500 BTUs and weighs about 4.24 pounds, which works out to roughly 21,600 BTUs per pound.

Dividing a heater’s rating by 21,600 gives its propane use in pounds per hour. A full 20 lb tank holds about 4.7 gallons, or roughly 430,000 BTUs, and the table below shows how long that lasts at common ratings.

How Long Does a 20 lb Propane Tank Last on a 40,000 BTU Patio Heater?

A full 20 lb tank runs a 40,000 BTU patio heater for a little under 11 hours on high, and about twice that at half power.

The 40,000 figure is the burner’s ceiling. The control valve meters how much gas reaches the burner, so turning the dial down cuts fuel use in step with heat output.

Low-setting output varies by model, so check the manual for your heater’s minimum rating.

How Long Does a 15 lb Propane Tank Last on a Heater?

A 15 lb propane tank runs a 40,000 BTU heater for about 8 hours on high and a 10,000 BTU tabletop heater for about 32 hours.

A 15 lb tank usually looks exactly like a 20 lb tank. Exchange tanks are the same size as the ones you’d refill, but some exchange programs stop filling at 15 lbs of propane.

The label on an exchange tank lists the net weight of propane inside, so a quick look tells you which fill you’re getting.

A fill station that refills by weight puts close to the full 20 lbs into the same tank. That’s a third more runtime per tank, which adds up fast for a restaurant swapping tanks every weekend.

How Long Do Larger Propane Tanks Last on Commercial Patios?

Larger tanks run a single 46,000 BTU patio heater for anywhere from about 14 hours on a 30 lb tank to 47 hours on a 100 lb tank.

The 33 lb size is commonly used with propane forklifts. However, forklift cylinders draw liquid propane, while patio heaters use vapor-service cylinders.

Most freestanding patio heaters are built to hold a 20 lb tank inside the base. The heater is tested and certified as a complete unit, regulator and hose included, and its burner is matched to the gas pressure that regulator delivers. Rigging a hose and fittings to reach a bigger tank changes that setup, and fire codes generally limit portable patio heaters to an integral tank of 20 lbs or less, so larger tanks suit only permanent, code-approved installations.

Why Do Patio Heater Propane Tanks Deliver Fewer Hours Than Expected?

Wind, cold weather, and small leaks can all cause a tank to deliver fewer hours than the BTU math predicts.

On a windy night, the heater’s warmth blows past guests instead of settling around the tables. Staff respond by cranking the dial to high, and the heater burns at its maximum rate all night. Placing heaters on the sheltered side of a patio—while keeping the clearances from walls and screens that fire codes and the manufacturer require—keeps the warmth where people sit.

Cold weather starves the burner rather than burning extra fuel. Propane has to boil off the liquid to reach the heater, and it boils at −42°C (−44°F), pulling heat from the tank walls to do it.

On a cold night with a low tank, less liquid touches the steel, vaporization slows, and the heater can drop below full output while propane still sloshes inside. Swapping to a fuller tank can help, though it won’t guarantee full output on a really cold night.

A slow leak at the regulator connection wastes fuel any time the tank valve is open. Brushing soapy water on the connection after every tank swap catches it. If you see bubbles, that means there’s a leak.

How Can You Tell How Much Propane Is Left in the Tank?

Weighing the tank gives an accurate reading of how much propane is left, while a warm-water test gives a rougher estimate.

Every tank has its empty weight stamped on the collar next to the letters TW, for tare weight. On a 20 lb tank it usually falls between 16 and 18 pounds. Subtract it from what the scale reads and you have the pounds of propane left.

A tank with a TW of 17 lbs that weighs 27 lbs holds 10 lbs of fuel. On a 40,000 BTU heater running high, that’s a little over 5 hours.

The warm-water test doesn’t require any tools. Pour a cup of warm water down the side of the tank, then run your hand over the same spot. The metal stays noticeably cooler wherever liquid propane sits behind it, so the line between cool and warm marks the fuel level.

How Many Propane Tanks Should You Keep on Hand?

Keep enough propane to cover each heater’s hourly draw times the hours you run it each week, plus at least one full spare.

A brewery running four 46,000 BTU heaters on high for 5 hours, Thursday through Sunday, burns about 170 lbs of propane a week. That works out to around nine 20 lb tanks or two 100 lb tanks. Medium settings bring the total down, but planning at the high setting covers the coldest nights.

Store spares upright and outdoors, away from the heaters, doorways, and anywhere customers walk.

Patio Heater Runtime Comes Down to Two Numbers

Runtime is based on pounds of propane in the tank and the BTU rating on the heater. With those two numbers in hand, the hours from any tank, whether a 15 lb exchange tank or a 100 lb tank, are a single division away.

Nick Vasco

Nick is an experienced B2B writer who brings his skill for crafting clear, easily digestible content to the industrial gas space.