The short answer
A heat pump moves heat from the air into the water, so it uses far less energy per BTU than burning gas, but its output falls as the air cools. A gas heater heats quickly in any weather but costs more to run. Size either with BTU per hour = gallons × 8.34 × degrees of rise ÷ hours.
Side by side
| Heat pump | Gas heater | |
|---|---|---|
| Running cost | Low | High |
| Heat-up speed | Slow | Fast |
| Best weather | Warm, above about 50°F air | Any |
| Install | 230V circuit (larger models) | Gas line and venting |
Examples
Heat pump: the Hayward HeatPro 140,000 BTU. Gas: the Pentair MasterTemp 400,000 BTU. The heater calculator shows how long each would take for your pool.
SafetyGas lines, venting and 230V circuits are jobs for licensed installers.
Products mentioned
Questions readers ask
Is a heat pump or gas heater better for a pool?
For holding temperature through a warm season, a heat pump; for occasional fast heating or cool weather, gas.
Do pool heat pumps work in cold weather?
Output drops as the air cools; most work best above about 50°F.