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Electric Pool Heat Pumps

How a pool heat pump works

Inside the cabinet is a refrigeration circuit. A large fan draws outside air across an evaporator coil, where cold refrigerant absorbs heat and turns to vapour. A compressor squeezes that vapour, raising its temperature. The hot refrigerant then passes through a heat exchanger, often a titanium or alloy coil, where pool water picks up the heat. The refrigerant expands, cools and returns to the evaporator. The unit is essentially an air conditioner whose hot side faces the pool.

COP and output

The coefficient of performance is heat delivered divided by electricity used. A COP of 5 means one kWh of electricity moves about 5 kWh worth of heat into the water. COP and output both rise with warmer, more humid air and fall as air cools. Makers often publish ratings at test points such as 80°F air with high humidity and 50°F air with moderate humidity. Compare models at the lower point if you swim in spring or fall. The pool heat pump size calculator estimates output needed at your air temperature.

Sizing

Because a heat pump adds heat slowly, sizing is mostly about holding temperature on the coolest nights you care about. Planning rules multiply surface area by the gap between target water and average air temperature, then by around 10 to 15 depending on wind. Undersized units run constantly and lose ground on cold nights. Oversized units cost more upfront and may need larger electrical service. A nightly cover cuts the needed size noticeably.

Electrical and placement

• A dedicated 240 V circuit with breaker, wire and disconnect sized from the nameplate, installed by a licensed electrician, with equipotential bonding as code requires.
• A level pad with the airflow clearances in the manual; recirculating cold discharge air reduces output.
• Somewhere the fan noise will not bother neighbours or bedrooms.
• Drainage for condensate, which can be significant on humid days and is sometimes mistaken for a leak.
• Plumbing usually after the filter and before any chlorinator.

Running habits that save money

Leave a heat pump running through the season rather than switching it off for weeks and asking for a large reheat. Use a cover every night. Run the pump schedule long enough to circulate water through the heater when heat is needed, often during the warmest part of the day when COP is best. Set a sensible target; each degree warmer adds noticeable cost. See the pool temperature guide.

Limitations

Most pool heat pumps stop or lose most of their output below an air temperature somewhere in the 40s or 50s Fahrenheit, depending on model and defrost design. They are not ideal for quick spa heating. Their slower heat-up surprises owners who expect gas-like speed. They also rely on refrigerant circuits; any refrigerant work requires a licensed technician.

Worked example

Figures below are illustrative examples (2026-10-29), not quotes or guarantees.

Assumptions: 450 sq ft pool, target 82°F, coolest swim month averages 62°F air, average wind, nightly cover. Need ≈ 450 × 20 × 12 × 0.7 ≈ 75,600 BTU/h output at 62°F. Over 150 run-hours a month at COP 4.5, electricity ≈ 75,600 × 150 ÷ (4.5 × 3,412) ≈ 739 kWh; at $0.15 per kWh, about $111 a month.

Maintenance

Keep the evaporator coil clear of leaves and grass clippings, rinse it gently if the manual allows, keep water balanced and book a professional check before the season. Corroded fins, ice that does not clear, unusual noise or tripped breakers need a technician; see pool heater not heating.

Compared with other options

Next to gas, a heat pump is slower but usually cheaper per BTU in mild air. Next to solar, it is more controllable and works on cloudy days but has an electricity cost. Our heat pump vs gas pool heater and solar pool heater guide explain more.

Reading a heat pump rating label

Rating labels and brochures often show two or three test points. A typical layout lists output and COP at warm, humid air, then at a cooler condition around 50°F, sometimes with water temperature stated too. The warm-air figure is the one in large print; the cool-air figure is the one that matters for spring and fall. Some labels also show input power in kW and running amps, which your electrician uses for circuit sizing. If you see only one rating, ask the dealer for the full performance table. A unit whose output drops sharply in cool air may be fine for a southern summer pool and disappointing for a northern one.

Defrost and cold-weather behaviour

When air is cool and humid, frost can form on the evaporator coil. Many units handle this by stopping the compressor and letting the fan melt the frost, while others reverse the refrigerant flow briefly to clear it faster. Either way, heating pauses during defrost, and output falls further as air gets colder. Most manufacturers state a minimum operating air temperature; below it the unit stops to protect itself. If you plan to swim when nights dip into the 40s, compare low-temperature performance and defrost features, or plan a backup heat source.

Heat pumps and pool chemistry

Many pool heat pumps use titanium or similar exchangers that tolerate chlorinated and salt water well, but all units list acceptable ranges for pH, alkalinity, hardness and salt. Out-of-range water can still damage seals or other parts and may void warranty. Install any automatic chlorinator after the heat pump with a check valve so concentrated chemicals do not flow back into it.

FAQ

Can a pool heat pump cool the pool?

Some models offer a reverse or chill mode; check the specification.

How loud is it?

Similar to a central air conditioner outdoor unit; look for published sound ratings and place it thoughtfully.

Can I plug it into an outdoor outlet?

No. It needs a dedicated hard-wired circuit installed by a licensed electrician.

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