Pool Heater Calculators — BTU, Time, Cost & Fuel Comparison

Quick answer

Shopping for a pool heater? Run the BTU calculator first — it returns the output BTU/hr your pool needs and converts it to the gas input rating on the box. Then check heating time, running cost or heat pump vs gas depending on where your decision stands.

Four calculators, one formula

Every tool on this site runs on the same published sizing physics — surface area × temperature rise × 12 for BTU output, gallons × 8.34 × rise for heat-up time, and the 82% federal minimum efficiency for converting gas input ratings. That's deliberate: brand calculators only ever run the math in their own favor, so their numbers can't be compared across brands. Ours can.

Pick the question you're actually asking:

How many BTUs do I need?

The main pool heater BTU calculator takes your pool's dimensions, target temperature, heat-up window and site conditions (wind, shade, solar cover) and returns the required output BTU/hr — plus the gas input rating to shop for, since gas heaters are sold by fuel burned rather than heat delivered. This is the tool to start with if you're shopping.

How long will it take to heat my pool?

The heating time calculator reverses the question: given a specific heater rating and your pool's volume, how many hours of running until you hit target? Useful for two very different moments — deciding whether a heater you already own is adequate, and checking whether the model in your cart will actually deliver a "swim by Saturday" promise.

What will it cost to run?

The running cost calculator prices a heater at your own fuel rates — $/therm for natural gas, $/gallon for propane, $/kWh for electricity — across a day, a month and a season, then shows cost per million BTU for every fuel type at your prices, so heat pump vs gas vs propane stops being folklore.

Heat pump or gas?

The heat pump vs gas calculator puts the same pool, the same season and the same energy demand through three fuel paths at once and shows the seasonal cost side by side — with the caveats that actually decide purchases: heat pump output collapses in cold air, gas wins fast heat-ups, propane prices swing.

Why the answers are comparable

Each calculator shows its full math under the result — every multiplication, every correction factor, every source — so you can check any figure by hand. The quick table on the homepage is generated from the same code as the calculators, and the sizing guide explains each constant with its source. Nothing on this site is a number we can't show the work for.

FAQ

Which calculator should I start with? The BTU calculator — every other answer depends on knowing the size of heater you're shopping for. Time, cost and fuel comparisons all take that figure as their input.

Are the calculators really brand-neutral? Yes — no manufacturer's sizing math is used anywhere. The formula, corrections and efficiency floor are the published industry rule and federal regulation, shown with sources under every result.

Do I need to sign up or pay? No. All four calculators are free, run in your browser, and nothing you type is sent anywhere — see the privacy policy. The full index of calculator articles lives at all calculators articles.

New to pool heating?

Start with the sizing guide for the physics in plain English, then run the calculators in order: BTU first, time second, cost third. The whole chain takes about five minutes and ends with a heater size, a realistic heat-up expectation and a seasonal budget you can defend.