What is the difference between a propane and natural gas pool heater?
The difference is the fuel and how it reaches the heater, not the heater itself. Most gas pool heaters (Pentair MasterTemp, Hayward Universal H-Series, Raypak) are sold in both a natural gas and a propane version, and many convert from one to the other with a kit. Inside, they are the same unit: a burner heats a copper heat exchanger the pool water flows through. The only real hardware difference is the gas orifices and the regulator, sized for each fuel's pressure and energy density. So the model you pick, the BTU rating, and how fast it heats do not change with the fuel.
What changes is the fuel's energy and how it arrives. Natural gas is mostly methane, delivered continuously through a utility line and measured in therms (100,000 BTU each) or cubic feet (about 1,030 BTU each). Propane is a denser liquid fuel stored in a tank on your property, carrying about 91,500 BTU per gallon. Because propane packs more energy per unit but costs more to buy, and natural gas is cheap but needs a pipe run to your house, the fuel you should choose is usually settled by what your property already has.
That is the crux: natural gas requires a utility line, and a large share of homes, especially rural and many suburban ones, simply do not have one at the street. Propane works anywhere because you bring the fuel to the site in a tank. If you are still choosing a heater type at all, weigh a heat pump against gas first, then size the unit you settle on with the pool heater calculator.
Is it cheaper to run a pool heater on natural gas or propane?
Natural gas is cheaper to run, usually by about half. Take a common 400,000 BTU heater. It burns about 4 therms of natural gas an hour, which at typical residential prices runs about $6 to $8 an hour. The same heater burns about 4.4 gallons of propane an hour (400,000 BTU divided by 91,500 BTU per gallon), which at common propane prices runs about $11 to $15 an hour. Propane costs more per unit of heat, so every hour the heater fires, propane costs more.
Prices swing with your region and the season, so treat those numbers as a ratio, not a quote. Natural gas rates are fairly stable; propane is a commodity you buy by the tank, and the per-gallon price drops if you pre-buy or fill in summer and spikes in a cold winter. Even at propane's best price it rarely beats natural gas per BTU. Where propane can win on cost is indirectly: if running a new gas line to your pad would cost thousands, a tank you already have or can rent makes more financial sense despite the higher fuel price.
Either fuel, the cheapest heat is the heat you do not lose. A solar cover cuts evaporation, which is where most pool heat escapes, and can halve a heating bill on either fuel. Right-sizing the heater to your water volume with the pool volume calculator keeps you from paying to run an oversized unit. And if you have not committed to gas at all, a heat pump costs far less per hour than either fuel in a warm climate; see gas vs heat pump.
How long will a 250 gallon propane tank last, and how is each fuel supplied?
A 250 gallon tank holds about 200 usable gallons, which is roughly 45 hours of full-fire heating for a 400,000 BTU heater. Tanks are filled to about 80%, so a 250 gallon tank gives you around 200 usable gallons, and the heater burns about 4.4 gallons an hour. Real-world run time stretches much further than that sounds, because you rarely run at full fire nonstop: heating a pool a few hours before weekend swims can use a tank over several weeks, while heating a large pool daily in cool weather can empty it in a week or two. Watch the gauge and schedule refills before you run dry.
Tank size matters for more than run time. A big heater draws propane fast, and a small tank cannot vaporize liquid propane quickly enough to keep up, especially in cold weather, when the tank frosts over and the flame starves. For a 300,000 to 400,000 BTU pool heater, most installers want a 250 or 500 gallon tank, not a small 100 gallon (420 lb) one. You can rent a tank through a propane supplier, often bundled with a fuel contract, or buy your own.
Natural gas has no tank and never runs out, which is its quiet advantage. It flows continuously from the utility, so you never monitor a gauge or schedule a refill. The one supply catch is the line itself: a 400,000 BTU heater needs a properly sized gas line, and tapping it onto an undersized line, or one already feeding a furnace, water heater, and range, can starve the heater and trip low-flame errors. Have the line sized for the added load when you install, and size the heater itself with the pool heater calculator.
Propane or natural gas: which pool heater should you buy?
Buy natural gas if you have or can affordably run a gas line to the pad; choose propane when you cannot. For most people the decision is made by the property, not preference. If your home already has natural gas service and the line can reach the pad without a costly trench, buy the natural gas version. It costs about half as much per hour to run, never runs out, and needs no tank taking up yard space. Over a few seasons the fuel savings dwarf any small difference in the heater itself.
Choose propane when natural gas is not available or would cost too much to bring in. That covers a lot of homes: rural properties, many suburbs off the gas grid, and pools set far from the house where extending a line means hundreds of feet of trenching. With propane you set a tank and you are running. You pay more per hour of heat, but you avoid a large one-time line cost and you can install almost anywhere.
Whatever the fuel, buy the same way: pick a reputable model in the right BTU size, and make sure it is configured (or professionally converted) for your fuel. Never run a heater on a fuel it is not set up for, because the orifices and regulator differ and the mismatch is dangerous. Size it to your water with the pool heater calculator, add a solar cover to cut the bill, and compare specific units in our best pool heater guide.
Propane wins on
- +Works anywhere: a tank means no utility line, ideal for rural and off-grid homes.
- +No costly gas line to trench and run to the pad; set a tank and go.
- +High energy density (about 91,500 BTU per gallon) and easy to add where gas will never reach.
Natural Gas wins on
- +Cheaper to run, usually about half the hourly cost of propane.
- +Never runs out: continuous utility supply, no tank to monitor or refill.
- +No tank on the property, more stable pricing, and lower long-term operating cost.
The verdict
Buy the natural gas version if your home has gas service and the line can reach the pad without an expensive trench. It costs about half as much to run (roughly $6 to $8 an hour against $11 to $15 for propane on a 400,000 BTU heater), never runs out, and needs no tank, so the fuel savings pay back quickly. Choose propane when natural gas is not available at your property or would cost thousands to bring in, which is the reality for many rural and suburban homes. The heater itself is the same either way and heats at the same speed, so let your gas supply decide the fuel, then size the unit with the pool heater calculator, cut the bill with a solar cover, and compare models in our best pool heater guide.
Related: Best pool heaters, Gas vs heat pump pool heater, Pool heater size calculator.
Frequently asked questions
Is it cheaper to run a pool heater on natural gas or propane?
Natural gas, usually by about half. A common 400,000 BTU heater burns about 4 therms of natural gas an hour (about $6 to $8) or about 4.4 gallons of propane an hour (about $11 to $15). Propane costs more per unit of heat no matter the season, so per hour of heating natural gas wins. Propane only makes better financial sense when running a new gas line to the pool would cost thousands, in which case a tank avoids that one-time expense. A solar cover lowers the running cost on either fuel.
How long will a 250 gallon propane tank last for heating a pool?
About 45 hours of full-output heating for a 400,000 BTU heater. A 250 gallon tank fills to roughly 200 usable gallons (tanks fill to 80%), and the heater burns about 4.4 gallons an hour. Real-world run time is longer than that sounds, because you rarely heat at full fire nonstop: a few hours before weekend swims can stretch a tank over several weeks, while heating a big pool daily in cool weather can empty it in a week or two. Watch the gauge and refill before you run dry.
What is the most economical way to heat a swimming pool?
A solar cover first, then the right heater for your climate. Most pool heat is lost to evaporation, so a cover can cut a heating bill by half or more no matter what you run. Among heaters, a heat pump is cheapest to run in a warm climate, natural gas is the cheapest fuel-burner, and propane costs the most per hour. Size the heater to your pool so you are not running an oversized unit; start with the pool volume calculator and pool heater calculator, and compare gas against a heat pump.
Is a propane pool heater worth it?
Yes, when natural gas is not an option. If your property has no gas line, a propane heater is the fastest, most reliable way to heat a pool on demand at any air temperature, and it installs anywhere you can place a tank. You pay more per hour than natural gas (about $11 to $15 versus $6 to $8 on a 400,000 BTU unit), so it is not the cheapest heat, but avoiding a costly gas line often makes it the sensible choice. If you already have natural gas at the house, buy that version instead.
Can you convert a natural gas pool heater to propane?
Usually yes, with the manufacturer's conversion kit and a pro to install it. Most major heaters (Pentair, Hayward, Raypak) are the same unit for both fuels, differing only in the gas orifices and regulator, so a kit swaps those parts and reconfigures the gas valve. Never run a heater on a fuel it is not set up for: the orifices are sized for a specific fuel and pressure, and a mismatch causes sooting, damage, or a dangerous flame. Have any conversion done and safety-checked by a qualified technician.