Pool Heater Finder: heat pump, gas, or solar — and what size?
Two questions decide a pool heater — which type (heat pump, gas, or solar) and what size — and most buying guides answer neither for your pool. Tell us your gallons, whether it's above- or in-ground, your region and swim season, and what matters most, and this hands you the type, the BTU to look for, the catch nobody mentions, and the showdown that ranks your actual options.
Find your pool heater
Tell us about your pool and what matters most. We'll name the right heater type, the size to look for, the honest catch, and the showdown that ranks your options — not a 20-screen article to wade through. Updates live.
Don't know your gallons? Work it out here →
Exact geometry at 7.48 gal/ft³. Kidney shapes, diving hoppers and salt/turnover figures live in the full Pool Volume Calculator.
👆 Set your pool and pick what matters to get your heater.
Don't know your gallons? Estimate from your pool's size
Rough estimate (rectangle ×7.5, oval ×6.7, round ×5.9 gal per sq-ft-ft; enter the diameter for a round pool). Need the exact number? The full pool volume calculator handles every shape and depth profile.
Sizing and picks come from the same research as our pool-heaters showdown — a starting point, not a permit. The heat model is FSEC's pool-loss physics (evaporation, convection and radiation from the surface, less the sun the water absorbs) run hour by hour on NOAA 1991–2020 hourly normals for your zone or the station nearest your ZIP, with NASA POWER sunlight and EIA energy prices. A heat pump delivers less heat as the air cools, so it does its work in the warm hours; solar only works while the sun's out; gas costs the most to run. Have a pro confirm the final BTU. Pool heaters generally don't earn a federal tax credit.
Heat pump or gas, by region and swim season
Same logic as the tool above, for a 20,000-gallon in-ground pool where the goal is the lowest running cost. For each month of the season it runs the zone's average day hour by hour (NOAA 1991–2020 hourly normals), works out what the pool loses through its surface less the sun it absorbs, and asks whether the heat pump we would size for this pool can replace that in the hours above 50°F. The second line in each cell is the same pool with a solar cover. Gas stays the answer for fast heat and spas; solar for near-zero running cost with patience.
| Region | Peak summer only Roughly Jun–Aug | Spring through fall Roughly May–Sep | As long as possible Into the shoulder months, Apr–Oct+ | Year-round Open all 12 months |
|---|---|---|---|---|
| Florida / Gulf Coast | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump covered: Heat pump |
| Southeast / South-Central | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Gas covered: Gas |
| Desert Southwest | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Gas covered: Heat pump |
| Coastal California | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump covered: Heat pump |
| Mid-Atlantic / Midwest | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Gas covered: Gas |
| Northeast / New England | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump (short in Apr) covered: Heat pump (short in Apr) | Gas covered: Gas |
| Pacific Northwest | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump (short in Apr) covered: Heat pump | Gas covered: Gas |
| Mountain / Upper Midwest / Far North | Heat pump covered: Heat pump | Heat pump covered: Heat pump | Heat pump (short in Apr, Oct) covered: Heat pump (short in Apr) | Gas covered: Gas |
What it costs to heat a pool, by climate zone
A 20,000-gallon in-ground pool (about 535 sq ft of surface), fenced, no cover, held at 82°F from May to September. The month columns are what the water settles at with no heater: the balance of what it loses through its surface to evaporation, air and sky (the Florida Solar Energy Center's pool-loss equations) against the sun it absorbs, hour by hour on each zone's NOAA 1991–2020 hourly normals and NASA POWER sunlight. The season bills use U.S. EIA residential averages (18.0¢/kWh, $1.87/therm natural gas, 2025-08 to 2026-07); the finder above swaps in your ZIP's weather and your state's prices.
| Climate zone | May unheated | Jun unheated | Jul unheated | Aug unheated | Sep unheated | Heat pump season | Gas season |
|---|---|---|---|---|---|---|---|
| Florida / Gulf Coast | 84°F | 88°F | 89°F | 89°F | 85°F | $0 | $0 |
| Southeast / South-Central | 79°F | 85°F | 87°F | 85°F | 79°F | $106 | $251 |
| Desert Southwest | 80°F | 84°F | 87°F | 87°F | 81°F | $61 | $143 |
| Coastal California | 75°F | 77°F | 80°F | 81°F | 78°F | $351 | $756 |
| Mid-Atlantic / Midwest | 72°F | 80°F | 84°F | 82°F | 75°F | $343 | $765 |
| Northeast / New England | 67°F | 76°F | 80°F | 78°F | 70°F | $711 | $1,511 |
| Pacific Northwest | 68°F | 73°F | 78°F | 76°F | 69°F | $803 | $1,708 |
| Mountain / Upper Midwest / Far North | 67°F | 77°F | 81°F | 78°F | 69°F | $700 | $1,509 |
What size heater for your pool
Starting-point sizing, straight from our heaters showdown. Heat pumps are sized to hold a temperature; gas heaters are sized to raise it fast — which is why the BTU numbers differ so much for the same pool. A screened pool or a windy, exposed one leans toward the next tier up. Have a pro confirm the final number.
| Pool volume | Heat pump | Gas heater |
|---|---|---|
| ~5,000 gal | 55,000–70,000 BTU | 200,000–250,000 BTU |
| ~10,000 gal | 55,000–70,000 BTU | 200,000–250,000 BTU |
| ~15,000 gal | 80,000–100,000 BTU | 200,000–250,000 BTU |
| ~20,000 gal | 110,000–130,000 BTU | 250,000–400,000 BTU |
| ~25,000 gal | 140,000–160,000 BTU | 250,000–400,000 BTU |
| ~35,000 gal | 180,000+ BTU | 400,000 BTU |
How long to warm a 20,000-gallon pool
Computed from the finder's own sizing tiers for a Florida in-ground pool in May (110,000 BTU heat pump, 250,000 BTU gas at ~84% efficiency; 8.34 BTU per gallon-°F, less what the pool keeps losing to the night air while it climbs, fenced, no cover). The finder above runs the same arithmetic for your gallons, target, weather and unheated water.
| Warm it by | Heat pump | Gas heater |
|---|---|---|
| +5°F | 7.9 hours · ~$8 | 4.0 hours · ~$19 |
| +10°F | 16 hours · ~$16 | 7.9 hours · ~$37 |
| +15°F | 24 hours · ~$24 | 12 hours · ~$56 |
| +20°F | 32 hours · ~$33 | 16 hours · ~$74 |
Solar is sized by panel area, not BTU: aim for panel area equal to about 50–100% of your pool's surface, toward the high end in a cooler climate — and about a third more again under a screen enclosure (Florida Solar Energy Center sizing).
How the finder decides
Type follows your goal, then your climate. Want fast heat, any-weather reliability, or a spa? That's gas — the only type that heats on demand in a cold snap. Want the lowest bills and you're patient? That's solar, when the sun cooperates. Otherwise — lowest running cost or a longer season — it's a heat pump whenever, month by month, the one we'd size for your pool can replace an average day's heat loss in the hours above 50°F, and gas when it can't in the middle of your season. A pool holds its heat overnight, so what matters is the warm part of the day, not the night low.
Size follows your gallons. A heat pump runs long to hold a temperature, so it's rated lower for the same pool; a gas heater is sized to raise the water fast, so its BTU number is much higher. Both scale with volume, and both get bumped up a tier for a screened or exposed pool that loses more heat.
The honest limits stay on the page. A heat pump's output falls away below ~50°F. Solar does nothing at night or under cloud. Gas costs the most to run. And pool heaters generally earn no federal tax credit — solar-pool heating is specifically excluded from the Residential Clean Energy Credit, and the 25C heat-pump credit expired at the end of 2025. We'd rather tell you than let a rosy calculator do the selling.
Then pick your model
Heat pump vs gas vs solar — the full showdown → ·Best in-ground heat pumps (by pool size) → ·Best budget heat pumps (small above-ground) → ·Best mid-size heat pumps (above-ground) → ·Coolers & reversible heat/cool →
FAQ
How long does it take to heat a pool?
It is arithmetic, not opinion: 8.34 BTU warms one gallon one degree, so a 20,000-gallon pool needs about 1,668,000 BTU to rise 10°F. On the heat-pump size we recommend for that pool (110,000 BTU rated, in Florida's May air, net of what the pool loses while it climbs) that is about 16 hours of continuous running; on the matching 250,000 BTU gas heater at ~84% efficiency, about 7.9 hours. Cold air slows a heat pump further and wind adds loss on top, which is why a heat pump is bought to hold a temperature and gas to reach one. The finder above computes it for your pool, your target, and your unheated water.
Gas or heat pump if I only swim on weekends?
Run the usage comparison in the finder: for a 20,000-gallon Florida pool heated from the 84°F our model puts it at unheated in May to 82°F for about eight days a month, gas from cold costs roughly $0 a month on fuel while a heat pump holding 82°F every day costs about $0 — so the "heat pump is always cheaper" rule quietly fails once you stop leaving it on. Leave it on most days (about $0 a month versus gas holding at $0) and the heat pump wins again. Speed is the other half: gas is ready in hours, a heat pump in a day or more.
What size pool heater do I need?
Size to your pool's volume, not "bigger is better." As a rough gas-heater guide: a pool up to ~15,000 gallons wants about 200,000–250,000 BTU, 15,000–25,000 gallons wants 250,000–400,000 BTU, and a large or windy, exposed pool wants 400,000 BTU. Heat pumps are rated in BTU too but sized to hold a temperature rather than blast heat — a ~140,000-BTU unit suits most average in-ground pools, and a 55,000-BTU unit covers a pool up to ~10,000 gallons. An undersized heater never quite gets there; an oversized one wastes money — have a pro confirm the number for your pool.
Heat pump vs gas vs solar — which is best?
They win on different things. A heat pump is far cheaper to run and is the default in warm climates, but it warms gradually and loses efficiency once the air drops below about 50°F. Gas heats fastest and works in any weather — the only type that beats a cold snap or runs a spa — but it costs the most to run. Solar has essentially no running cost, but it only adds heat while the sun is out. Pick the heat pump for low cost in mild weather, gas for speed and cold, and solar for the lowest bills if you get reliable sun and you're patient.
At what temperature does a pool heat pump stop working?
A pool heat pump pulls warmth out of the surrounding air, so its output falls as the air cools: Pentair, Hayward, AquaCal and Jandy's own rating tables show about two-thirds of the rated heat at 50°F air, and the Department of Energy put the efficient range above 45–50°F. That is why heat pumps are the default in Florida and the Sun Belt, and why they suit a northern pool used from May to September. A pool holds its heat overnight, so the heat pump does its work in the warm hours: even in a northern April or October it can replace most of an average day's loss, and a solar cover closes the rest. Owners who want to swim through the winter, or need heat fast, are the ones who need gas.
Does a screened (caged) pool change which heater I need?
Yes. Florida Solar Energy Center testing measured a standard screen enclosure blocking 30–40% of the solar energy reaching the pool on a clear day, so a caged pool runs noticeably cooler through fall and spring and leans on the heater more than an open one. Heat pumps and gas heaters work the same under a cage — they just have a bigger gap to close. If you go solar, plan for about a third more panel area than an identical unscreened pool.
Do pool heaters qualify for a tax credit?
Usually not. Pool heaters generally don't qualify for federal energy tax credits, and solar pool heating is specifically excluded from the federal Residential Clean Energy Credit (that solar credit is for heating your home, not your pool). The federal 25C heat-pump credit also expired at the end of 2025. Some local utilities offer their own rebates on efficient pool equipment, so it's worth checking yours — but don't count on a federal write-off.