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Run time tells you how many hours a tank lasts. It does not tell you what that costs. Here is the math that converts hours into dollars, using your own local propane price rather than a number that goes stale the moment it’s published.
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Why We Don’t Quote a National Average Price
Propane price per gallon varies a lot by region, season and whether you’re refilling versus exchanging a tank. A number that’s accurate today can be out of date within a season. Instead of quoting a figure that will drift, this guide shows you the formula, with a clearly labeled example, so you can plug in your own local price and get an accurate answer.
The Formula
Propane holds roughly 91,500 BTU of usable energy per gallon. A gallon of propane weighs about 4.24 lb, which works out to roughly 21,600 BTU per pound — the same figure used throughout our run-time guides. To find your cost per hour, follow these steps: convert your local price per gallon to a price per pound, then figure out how many pounds per hour your heater burns, then multiply the two.
A Worked Example (Using a Hypothetical Price)
Say propane costs $3.00 per gallon where you buy it — check your own local price, since this is only an example. Divide $3.00 by 4.24 lb per gallon, which gives roughly $0.71 per pound. A 9,000 BTU heater burns about 0.42 lb per hour (9,000 divided by 21,600). Multiply $0.71 by 0.42, and you get roughly $0.30 per hour to run that heater at full output. Run the same heater on a lower setting, and the cost per hour drops proportionally.
Cost Comparison Across BTU Tiers
Using the same $3.00-per-gallon example price: a 3,800 BTU heater costs roughly $0.12 per hour. An 18,000 BTU heater costs roughly $0.59 per hour. A 60,000 BTU forced-air heater costs roughly $1.98 per hour. Higher BTU output means a heater burns fuel faster, so the cost per hour scales with output, not with tank size.
Why Tank Size Doesn’t Change Cost Per Hour
A bigger tank changes how often you refill, not how much fuel your heater burns per hour. Cost per hour depends entirely on your heater’s BTU output and your local propane price. A 20 lb tank costs more to fill than a 1 lb cylinder, but it also holds roughly 20 times the fuel, so the cost per hour of actually running the heater stays the same either way.
Refill vs. Exchange Changes the Real Number
Exchanging a tank at a hardware store or gas station typically costs more per gallon than filling your own tank at a dedicated refill station, since exchange pricing includes a convenience and tank-swap premium. If you’re calculating running cost seriously, use your actual refill price, not the exchange price, if you have access to a refill station. Our tanks and accessories guide covers this tradeoff in more depth.
How Your Chosen Setting Changes the Real Cost
Most of the examples above assume a heater running at its full, maximum BTU output, since that gives the highest and easiest-to-calculate cost-per-hour figure. In practice, many owners run their heater on a lower setting for most of a session, stepping up to full output only when conditions genuinely call for it, and the cost drops roughly in proportion to how far below maximum output the heater is actually running. A heater spending most of an evening on its lowest setting, with only occasional bursts at full output, will cost meaningfully less over that evening than the flat full-output figure suggests, which is one more reason the habit of starting low and stepping up only when needed pays off in dollars, not just in stretched fuel.
Estimating Cost Over a Full Season
Once you know your cost per hour, multiplying it by your typical hours of use per week, and then by the number of weeks in your heating season, gives a rough seasonal total worth comparing against other heating options. A heater used for three hours a night, three nights a week, across a twelve-week cold season adds up to 108 hours of runtime, which you can multiply directly by your cost-per-hour figure from the formula above. This kind of seasonal estimate is far more useful for budgeting than a single per-hour number in isolation, since it reflects how the heater is actually used rather than a one-off snapshot.
Using This Alongside the Run-Time Calculator
Once you know your cost per hour, multiply it by your expected run time to get a cost for a whole evening, trip, or job. The calculator below estimates run time by tank size and heater BTU. Combine that number with your own cost-per-hour figure from the formula above for a complete picture of what a heating session actually costs.
Comparing Cost Across Different Heater Models
When you’re weighing two heaters at different BTU tiers, running the cost formula for both, at your own local propane price, gives a clearer picture than comparing BTU numbers alone. A lower-BTU heater that adequately covers your space will almost always cost less to run over a season than a higher-BTU model doing the same job, since it burns less fuel per hour for the same result. This is one more reason sizing correctly, rather than buying more BTU than you need "to be safe," pays off in ongoing cost, not just in upfront price.
Rounding Errors and Why Small Differences Add Up
A few cents difference in cost per hour looks trivial in a single calculation, but multiplied across a full heating season it becomes a real number. A heater costing an extra $0.20 per hour, run for 100 hours across a season, adds $20 to your fuel bill compared to a more efficiently sized alternative. That is not a large sum on its own, but it illustrates why the per-hour formula on this page is worth running properly rather than eyeballing, especially before committing to a specific model or tank size for regular seasonal use.
Propane Run-Time Calculator
Estimate how long a tank will last. Real-world run time varies with weather, altitude and burner setting.