A Florida pool is warm for most of the year without any help. The question is what to do about the 4–6 months when it isn't, and how to pay for that decision over the next decade. There are three mainstream heater types on the market, each with a clear use case. Pick wrong and you'll either be cold six months a year or watch the gas meter spin harder than the pool pump.
The three heater types, in plain English
| Type | How it heats | Speed | Operating cost |
|---|---|---|---|
| Gas (natural or propane) | Burns fuel under a heat exchanger. | Fast — raises a 15,000-gal pool roughly 2–3°F per hour at 400k BTU on paper. | High per hour. Best for short, intense use. |
| Heat pump (electric) | Moves heat from the outside air into the water, like an AC run in reverse. | Slow — about 12 hours on paper to raise a 20,000-gallon pool 10°F with a 140k unit, and a day or more in real conditions. | Low per hour. Typically 3–8x more efficient than electric resistance. |
| Solar | Pumps pool water through black panels in direct sun. | Weather-dependent. Gains 5–10°F on a good day. | Essentially free after install. No fuel, minor pump energy. |
How to pick, Florida edition
- Heat pump is the default answerfor most Florida residential pools. Our mild winters keep ambient air above ~55°F on most days — the temperature floor below which a heat pump's efficiency tanks. You trade a slower heat-up for the lowest running cost of any heater that works in any weather (solar is cheaper to run, but it depends on your roof and the sun).
- Gas makes sense when you use the pool rarely but want it hot fast— weekend homes, vacation rentals, or when a cold snap hits a heat pump harder than the owner wants to wait out.
- Solar is a great supplement, rarely a standalone answer. Pair solar with a heat pump to extend the season for pennies and only run the heat pump on cloudy days.
- Electric resistance heaters (other than small spa-only units) are a Florida anti-pattern. Slow, expensive, and outclassed by heat pumps in every way that matters.
Comparing specific models? Capacity, efficiency, heat exchanger and warranty for every Hayward, Pentair, Jandy, Raypak, AquaCal and other heater we install are side by side in our pool heater comparison, each with its manufacturer sources.
Sizing — the math that protects your budget
Under-sizing a heater is the single most common mistake on Florida pool builds. The rule of thumb pool builders use:
- BTU = Gallons × 8.33 lb/gal × desired °F rise— the one-time energy to raise the pool to temperature.
- Divide BTU by the heater's output and by the hours you're willing to wait to get heat-up time.
- Add 4% for every 1,000 ft above sea level. Irrelevant in most of Florida; matters in Orlando's higher elevations barely.
For a 20,000-gallon pool rising 10°F: 20,000 × 8.33 × 10 = 1,666,000 BTUof total energy needed. On paper, a 400,000 BTU/hr gas heater delivers that in about 4 hours (nameplate input; at roughly 82% efficiency, allow closer to 5). A 140k BTU/hr heat pump does it in about 12 hours at its rated output in 80°F air, and a day or more in real winter conditions.
The COP conversation (for heat pumps)
Coefficient of Performance (COP) is the ratio of heat output to electrical energy consumed. An electric resistance heater has a COP of 1 — one unit of electricity delivers one unit of heat. A modern pool heat pump is AHRI-rated at COP 5–6 (80°F air, 80°F water; some inverter units approach 6.5 at ideal conditions), which means for the same electricity bill you get 5–6 times the heat. Colder air lowers COP; scroll-compressor units keep performance higher at cold ambient than older reciprocating designs.
Bottom line for most Florida homeowners: size a heat pump for your pool, consider adding solar if your roof works, and only go gas if you genuinely need to heat a cold pool on short notice a few times a year.
Watch: Why pool heaters are not rated by how hot they get
How heater capacity relates to heating speed, pool size, and the plumbing flow available to the equipment.
Pool heater sizing calculator
Surface area × temperature rise × 12 = required heater output. Surface area drives it — evaporation is where pools lose heat.
84–88°F is the family sweet spot.
South Florida unheated pools sit in the low-to-mid 70s most winters and can dip into the 60s after a hard cold front; size for the cold weeks.
Gas heater: 200k BTU nameplate
A 19°F rise on 392 sq ft needs ≈ 89,000 BTU/hr of output (≈ 109k input at ~82% efficiency). Oversizing a gas heater is fine — it just reaches temperature faster. Undersizing means it runs forever on cold weekends. Heat pumps are rated differently (typically 110k–140k BTU output) and heat slower but far cheaper per degree — the right call for set-and-hold temperature in South Florida; gas wins for fast weekend heat-ups.
Reference sizing for an uncovered residential pool with typical wind exposure, per manufacturer surface-area charts. A solar cover cuts the real load dramatically. Final sizing and gas-line capacity are the installer's responsibility.
Book heater service·Get a heater sized and installed·My heater needs repair
Frequently asked questions
Gas is the fast option. A 400,000 BTU gas heater raises a 15,000-gallon pool roughly 2 to 3 degrees an hour on paper, less on a windy night, and for a 20,000-gallon pool needing a 10-degree rise it delivers the full heat-up in about 4 hours. A heat pump is slow by comparison: a 140k BTU heat pump does that same 20,000-gallon rise in about 12 hours on paper at its rated output, and a day or more in real winter conditions. Gas wins on speed, heat pump wins on running cost.
Run the math builders use: BTU equals gallons times 8.33 pounds per gallon times the desired degree rise. That is the one-time energy to bring the pool up to temperature. For a 20,000-gallon pool rising 10 degrees, that is 1,666,000 BTU total. Divide that by the heater's output and by the hours you are willing to wait to get heat-up time. Add 4 percent for every 1,000 feet above sea level, which barely matters anywhere in Florida. Under-sizing is the most common mistake on Florida builds.
COP is Coefficient of Performance, the ratio of heat output to the electricity the unit burns. An electric resistance heater has a COP of 1, so one unit of electricity gives you one unit of heat. A modern pool heat pump is AHRI-rated at COP 5 to 6 at 80-degree air and water, with some inverter units pushing near 6.5 in ideal conditions. That means 5 to 6 times the heat for the same power bill. Cold air drops COP, and a scroll-compressor unit holds performance better in cold ambient than an older reciprocating design.
Rarely. Solar pumps pool water through black panels in direct sun and gains 5 to 10 degrees on a good day, and it is essentially free to run after install with no fuel and only minor pump energy. The catch is it is weather-dependent, so it is a great supplement, not a standalone answer. The move that works is pairing solar with a heat pump: solar extends the season for pennies and you only fire the heat pump on cloudy days.
Our mild winters do the heavy lifting. On most days the ambient air stays above roughly 55 degrees, which is the temperature floor below which a heat pump's efficiency tanks. Stay above it and you get the lowest running cost of any heater that works in any weather (solar is cheaper to run but depends on your roof and the sun), typically 3 to 8 times more efficient than electric resistance. You trade a slower heat-up for that low operating cost, which is the right trade for a pool you keep warm through the season rather than firing hot on short notice.
A Florida pool is warm for most of the year without any help. The real question is what to do about the 4 to 6 months when it isn't, and how you want to pay for that decision over the next decade. That short cold window is exactly why a heat pump fits most homeowners: you keep the pool comfortable through the cool months at the lowest running cost, and only lean toward gas if you need a cold pool hot fast a handful of times instead of holding temperature all season.
Not sure your heater is the right one for your pool?
We diagnose and repair heat pumps, gas heaters, and solar across Palm Beach and Broward, and we tell you honestly when a unit is undersized or done. Quoted in writing before any part is ordered.