Pool Heat Pumps: Cost to Run and How to Size One

A pool heat pump extends your swim season by pulling warmth from the outside air and moving it into the water, and it costs far less to run than gas. Expect to pay around $2,500 to $6,000 installed for the unit, and roughly $100 to $400 a month to run it during swim season, depending on your climate, pool size, and how warm you keep the water. Sizing comes down to your pool’s surface area and the temperature rise you want, not a rough square-foot rule.

What a pool heat pump actually is

A pool heat pump is the same core technology as the air source heat pump that heats a house, tuned for water instead of air. A fan pulls outdoor air across a coil, the refrigerant inside absorbs that heat, a compressor concentrates it, and a heat exchanger passes it into pool water flowing through the unit. It does not burn fuel to make heat. It moves heat that already exists in the air, which is why it can deliver several units of heat for every unit of electricity it draws.

That ratio is the whole point. A gas pool heater is roughly 80 to 90 percent efficient, meaning you always get less heat than the energy in the gas. A pool heat pump runs at a COP of about 5 to 6 in mild weather, meaning five to six units of heat per unit of electricity. The tradeoff is speed: a heat pump warms water slowly and steadily, while gas blasts heat on demand. For most homeowners who keep a pool warm across a season, slow and cheap wins.

What it costs to buy and install

The unit itself usually runs $1,800 to $4,500 depending on capacity and whether it has an inverter compressor. Installation adds $500 to $2,000 on top, covering the concrete pad or mounting, plumbing tie-ins to your filter loop, and the electrical circuit. Most residential pool heat pumps need a dedicated 240-volt circuit, and if your panel is full or far from the equipment pad, the electrical work can be the biggest single line item.

* Ranges assume a standard equipment pad within reach of an existing 240V circuit. Long electrical or plumbing runs push costs higher.

What it costs to run

Running cost is where a heat pump earns its keep. A typical residential unit draws about 5 to 8 kilowatts while the compressor runs. At an average US electricity rate, that is roughly $0.75 to $1.50 an hour of actual run time. It does not run around the clock once the water is at temperature; it cycles to hold the setting and to make up for overnight heat loss.

Over a month of active swim season, most owners in a mild climate spend somewhere around $100 to $300 to hold a pool in the high 70s to low 80s Fahrenheit. Push the water into the mid 80s, run late into the fall, or fight windy uncovered evaporation, and monthly cost can climb past $400. Three things move that number more than anything else:

• Target temperature. Every degree warmer costs real money. Going from 80 to 84 degrees can raise energy use by 20 to 40 percent because heat loss accelerates with temperature.
• A cover. An uncovered pool loses most of its heat to evaporation overnight. A solar or thermal cover is the single highest-return upgrade you can pair with a heat pump, often cutting run cost by a third or more.
• Outdoor air temperature. Like any air-source system, output and efficiency drop as the air cools. Below about 45 to 50 degrees Fahrenheit, most standard pool heat pumps lose enough capacity that they run long and inefficiently, and some shut off entirely.

A pool cover does more for your running cost than any brand choice on the equipment pad.

How to size one

Pool heat pumps are rated in BTU per hour of heat output, the same unit used for home systems where 1 ton equals 12,000 BTU/h. Unlike a home system, where you would insist on a Manual J load calculation, pool sizing is driven mainly by three inputs: surface area, desired temperature rise, and how fast you want to hit temperature.

The surface-area rule of thumb

Surface area matters more than volume because most heat escapes off the top of the water. A common starting point is to divide the pool’s surface area in square feet by a factor tied to how many degrees of rise you want. For a modest 10 to 15 degree rise in a mild climate, many installers land on roughly 4 to 6 BTU/h per gallon, which puts an average 20,000 gallon pool around 90,000 to 120,000 BTU/h. Colder regions, shorter heat-up expectations, and windy sites all push you toward the larger end.

Do not undersize to save money

An undersized heat pump never quite catches up. It runs continuously, struggles to hold temperature on cool nights, and costs more over a season because it operates at its least efficient point constantly. Oversizing a pool heat pump is far less harmful than short-cycling a home system, so when in doubt, size up rather than down. A larger unit reaches temperature faster and then coasts on short cycles to hold it.

How to choose a good one

Most residential pool heat pumps come from a handful of established pool-equipment makers, and the meaningful differences are fewer than the marketing suggests. Focus on four things rather than chasing a single best model.

• Right-sized BTU output for your pool and climate, based on the sizing logic above. This matters more than any feature.
• Inverter versus single-stage. An inverter compressor varies its speed, runs quieter, and holds temperature more efficiently at part load. It costs more up front but usually pays back in run savings and comfort. A single-stage unit is cheaper and simpler.
• Titanium heat exchanger. This is the part that touches pool water, and titanium resists corrosion from chlorine and salt far better than cheaper metals. It is close to standard now, but confirm it, especially for a saltwater pool.
• Cold-weather capability if you want a long shoulder season. Some units are engineered to keep producing useful heat into the 40s Fahrenheit, similar in spirit to the cold-climate models used for whole-home heating.

Heat pump versus gas versus solar

The three common pool heating options each fit a different priority. A gas heater wins on raw speed and works in any weather, but running cost is high and climbs with fuel prices. A pool heat pump costs more to buy than a comparable gas unit but far less to run, as long as your daytime air stays mild. Solar pool heating has the lowest running cost of all, essentially free once installed, but it only works when the sun is out and needs significant roof or ground area.

* Many owners pair a heat pump for daily warmth with a solar cover to slash losses, which gets close to the best of both.

If you like understanding the underlying physics, it is the same cycle described in how heat pumps work, and the efficiency terms carry over from heat pump efficiency. The difference is that pool ratings lead with COP and BTU output rather than the SEER2 and HSPF2 numbers you see on home equipment.

Installation and upkeep

A pool heat pump goes on a level pad with clear air space around it, typically a couple of feet on each side and open sky above, because it needs to breathe outdoor air the way a home condenser does. It plumbs into the return side of your filter loop after the pump and filter, so clean, pressurized water flows through the exchanger. Placement rules echo the ones in our heat pump installation guide: give it airflow, keep it out of tight corners, and mind the noise near patios and neighbors.

Maintenance is light. Keep leaves and debris out of the fan, hose the coil clean once or twice a season, maintain proper water chemistry so the exchanger does not scale or corrode, and winterize the unit by draining it in freezing climates. Done consistently, that is most of what stands between you and a 10 to 15 year service life.

Is a pool heat pump worth it?

For most homeowners in a warm or mild region who want to swim comfortably from late spring into fall, yes. The higher purchase price over a gas heater usually pays back within a few seasons through lower running cost, and a heat pump keeps water at a steady, pleasant temperature without the fuel bill spikes. It is the wrong tool if you need to heat a pool fast on a cold day, run a spa year-round, or live somewhere the swim season air stays below the 40s, where output falls off. Pair the right-sized unit with a cover, keep your target temperature honest, and a pool heat pump is one of the cheapest ways to run a heated pool.

Frequently asked questions