Why a Heat Pump Is Cheap to Run
A pool heat pump doesn't create heat — it moves it, pulling warmth out of the outside air and transferring it into the water, the same trick a fridge uses in reverse. That's why it's so efficient: for every unit of electricity it draws, it delivers several units of heat into the pool.
That ratio is the COP (coefficient of performance), and pool heat pumps typically run a COP of about 3.5 to 5.0 — roughly 350–500% "efficient" compared with the electricity they use. The catch is that a heat pump needs warm-ish air to harvest: its COP drops as the air cools, and below about 50°F it becomes slow and inefficient. It's a warm-season heater, not a deep-winter one.
The Running-Cost Math
Your cost comes down to three things: how much electricity the unit draws (kilowatts), how many hours it runs, and your electricity rate. The formula is simple:
kW drawn × hours run × your $/kWh = cost
A worked example: a mid-size heat pump draws roughly 5 kW of electricity. Run it 8 hours to heat up at an electricity rate of $0.15/kWh, and that day costs about 5 × 8 × $0.15 = $6. Once the pool is at temperature, a cover holds most of the heat and daily top-up runtime drops sharply. Plug your own unit's kW draw and local rate into the numbers — those two vary enormously by pool and region, which is why a single "it costs $X a month" figure online is close to meaningless.
Get Your Actual Numbers
The heating-cost calculator uses your pool size, target temperature, and local energy rate to estimate real running cost — and the heater-size calculator makes sure the unit is the right size to begin with.
What Actually Drives Your Bill
Target temperature
Every extra degree costs more heat to reach and hold. Dropping your target even a couple of degrees noticeably cuts the bill.
Air temperature
A heat pump is most efficient in warm air. Cool nights and cool shoulder-season days push COP down, so the same target costs more to hold.
Evaporation and wind
Most of a pool's heat loss is evaporation off the surface. An exposed, windy pool bleeds heat constantly — which the heater has to keep replacing.
The Cover Changes Everything
If you take one thing from this guide: a cover is the single biggest lever on heating cost. Because most heat escapes by evaporation from the water surface, a solar blanket or cover that sits on the water dramatically slows that loss. Owners routinely cut heating runtime — and bill — by a large fraction just by covering the pool overnight and when it's not in use.
Without a cover, your heat pump spends much of its time replacing heat that's evaporating straight into the air. A cover keeps that heat in the water, so the pump runs less to hold the same temperature. It pays for itself faster than almost any other upgrade.
Heat Pump vs Gas Heater
A gas heater fires up fast and heats regardless of air temperature, so it wins for on-demand heat and cold weather — but you pay for every therm it burns, and it has no efficiency multiplier. A heat pump is far cheaper to run for regular season-long heating thanks to that 3.5–5.0 COP, but it's slow to heat and fades in cold air.
Rule of thumb: heat pump for keeping a pool warm all season economically; gas for fast, occasional, or cold-weather heating. Many owners in mild climates run a heat pump as the workhorse. Size it right first — an undersized unit runs constantly and never quite gets there, and the BTU number is worked out the same way for either type in what size pool heater do I need. If you are choosing between the two rather than just running one, the heat pump vs gas payback calculator puts your own fuel prices and installed quotes against each other and returns the number of seasons it takes to break even.