How long does a 20 lb propane tank last in a fire pit, and what does it cost per hour?

Gas fire pit tables are the fire feature most Pacific Northwest buyers end up with, partly because gas is the fuel most often still allowed when wood is banned (see our summer burn ban guide). Makers publish a burner rating in BTU per hour. Almost none publish how long a tank lasts or what an evening costs. This guide does that math from federal and industry figures so you can do it for any burner.

The three numbers you need

• Your burner's rating in BTU per hour at full flame. It is on the spec sheet or rating plate. Outdoor GreatRoom, for example, lists 55,000 BTUs for the Crystal Fire Plus burners in its Brooks, Cove and Stonefire tables.
• The energy in the fuel. The Propane Education & Research Council (PERC) lists propane at 21,548 BTU per pound and 4.2 lb per gallon of liquid at 60°F. EIA lists 91,452 BTU per gallon of propane and 1,036 BTU per cubic foot of natural gas.
• How much propane is really in the tank. NIST explains that a "20 lb" cylinder is named for the most propane it can safely hold, and that most 20 lb cylinders are filled and labeled to a net 15 lb. Blue Rhino states its grill tanks hold a net 15 lb. A cylinder spec sheet from USA Cylinder lists the 20 lb size at 4.7 gallons of LPG capacity, which is how much a station can put in when it fills to the limit.

Run time in hours = pounds of propane x 21,548 / burner BTU per hour. Gallons per hour = burner BTU per hour / 91,452.

Run time by burner size (full flame)

Our arithmetic from the PERC and EIA figures above. These are best-case numbers at the highest setting. Most people run the flame lower once the fire glass is hot, which stretches the tank.

What this means in practice: with a 55,000 BTU table and an exchange tank, three two-hour evenings at full flame use up the tank. Keep a spare if you entertain. Large custom burners of 100,000 BTU and up are usually piped to natural gas or a large tank for this reason.

Why the flame fades on cold nights

A cylinder only delivers gas as fast as the liquid inside can boil off into vapor, and it takes the heat for that from the surrounding air. PERC's technical guide says the vaporization rate falls when the outside air is colder or the container has less liquid in it, and that frosting on a tank acts as an insulator and lowers it further. On a 38°F evening in Seattle or Portland, a big burner on a small, half-empty cylinder can lose flame height well before the tank is empty. Practical fixes: start the evening with a fuller tank, run the burner lower, or move to a larger tank or natural gas. Do not heat a cylinder, and follow the fire pit maker's manual for any larger tank or remote tank setup, since many tables are designed around a 20 lb cylinder in the base.

Cost per hour: propane vs natural gas

Propane is sold to homes two ways, and the price per gallon differs a lot. EIA tracks the price of bulk propane delivered to homes for heating. For the week of October 19, 2026 the U.S. average was $2.689 per gallon. EIA does not publish a Washington or Oregon residential propane figure in that weekly table. Cylinder refills and exchanges are usually priced higher per gallon than bulk delivery, and an exchange tank holds about 3.6 gallons (15 lb / 4.2 lb per gallon). To get your real price per gallon on an exchange, divide what you paid by 3.6.

Natural gas math: cubic feet per hour = burner BTU / 1,036. A 55,000 BTU burner uses about 53 cubic feet an hour, or 0.053 Mcf. EIA's average residential prices fold fixed monthly charges into the per-unit price, and they move with the season: the July 2026 residential average was $25.72 per Mcf in Washington and $23.23 in Oregon, which would put the same burner at about $1.37 and $1.23 an hour. The extra gas a fire pit uses is billed at your utility's per-therm rate, so your bill is the best guide. One Mcf is about 10.36 therms at EIA's 1,036 BTU per cubic foot.

Worked example for an exchange tank: if you pay $25 for a 15 lb exchange, that is about $7.00 per gallon, and a 55,000 BTU burner at full flame costs about $4.25 an hour. (That $25 is an example, not a quoted price. Use your own receipt.)

Should you convert to natural gas?

Many gas tables can switch fuels. Outdoor GreatRoom says its Brooks, Cove and Stonefire tables ship set up for liquid propane with a natural gas conversion kit included. Natural gas makes sense when you burn often, already have gas at the house, and want the pit in one fixed spot. Propane makes sense for a table you may move, a rental, or an occasional fire. Running a new gas line generally needs a permit and a qualified installer; our wood vs gas vs smokeless guide covers the permit side, and how far a fire pit must be from a house covers placement.

Tank safety basics

• Propane vapor is heavier than air. NIST notes that when released it flows to the lowest point, such as drains and basements, so store spare cylinders outside and never in a basement or house.
• Use the cylinder size and hose the fire pit maker specifies, and leak-test connections the way the manual describes before each season.
• A burn ban that allows gas does not override your fire pit manual or local fire code clearances. Check both.

Sources

All pages checked October 22, 2026. Run times and costs are our arithmetic from the figures in these sources.

• U.S. Energy Information Administration: British thermal units (propane 91,452 Btu per gallon, natural gas 1,036 Btu per cubic foot)
• EIA: Natural gas prices by state, annual (2025 residential price, Washington and Oregon)
• EIA: Natural gas prices by state, monthly (July 2026 residential price)
• EIA: Weekly heating oil and propane prices, residential propane (released October 21, 2026)
• Propane Education & Research Council: The Propane Technical Pocket Guide (properties table and vaporization rates)
• NIST Office of Weights and Measures: Liquified Petroleum Gas 20 Pound Cylinders
• Blue Rhino: How much propane does Blue Rhino put in its tanks?
• USA Cylinder: Propane cylinders spec sheet (20 lb cylinder, 4.7 gallon LPG capacity)
• Outdoor GreatRoom Brooks Round gas fire pit table (55,000 BTU, 20 lb tank in base, NG conversion kit)
• Outdoor GreatRoom Stonefire gas fire pit table
• Outdoor GreatRoom Cove Round gas fire pit table

Related guides

• The best fire pits of 2026, ranked by use case
• Can you use a propane fire pit during a summer burn ban in Washington or Oregon?
• Wood vs gas vs smokeless fire pit
• Washington burn bans and fire pits
• Fire pit burn restrictions in Portland, Eugene and Vancouver
• Running a natural gas line to a fire pit in Seattle or Portland

Frequently asked questions

How long does a 20 lb propane tank last in a fire pit?

At full flame on a 55,000 BTU burner, a cylinder holding the full 20 lb of propane lasts about 7.8 hours, and a typical exchange cylinder filled to 15 lb lasts about 5.9 hours. That is our arithmetic from the Propane Education & Research Council figure of 21,548 BTU per pound. Turn the flame down and the tank lasts longer; cold weather and a nearly empty tank can make the flame drop before the tank is truly empty.

Is an exchange tank really 20 pounds of propane?

Usually not. NIST says the "20 lb" name is the most propane the cylinder can safely hold, but most 20 lb cylinders in exchange programs are filled and labeled to a net 15 lb. Blue Rhino states its grill tanks contain a net 15 lb. A refill at a station that fills to capacity can put in up to about 4.7 gallons, which is about 20 lb.

What does it cost per hour to run a propane fire pit?

Divide the burner rating by 91,452 BTU per gallon (EIA) to get gallons per hour, then multiply by what you pay per gallon. A 55,000 BTU burner on high burns about 0.6 gallons an hour. At the EIA U.S. average residential propane price of $2.689 a gallon (week of October 19, 2026) that is about $1.62 an hour, but that price is for bulk delivered propane. Cylinder refills and exchanges usually cost more per gallon, so use your own receipt.

Is natural gas cheaper than propane for a fire pit in Washington or Oregon?

Per hour of flame, usually yes at EIA average prices. A 55,000 BTU burner on natural gas uses about 53 cubic feet an hour. At the 2025 EIA average residential prices ($17.62 per thousand cubic feet in Washington, $16.71 in Oregon) that is roughly $0.94 an hour in Washington and $0.89 in Oregon. The catch is the up-front cost of a gas line, a permit and a licensed installer, and the fact that you cannot move the pit.

Why does my fire pit flame get weak in cold weather?

A cylinder turns liquid propane into vapor using heat from the air around it. The Propane Education & Research Council says the vaporization rate drops when the outside temperature is lower or the container has less liquid in it. On a cold Pacific Northwest evening a large burner on a small, low tank can sputter before the tank is empty. A fuller tank, a lower flame setting or a larger tank helps.

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