Heat pumps move heat from the air into the water, so they cost much less to run but heat slowly and lose output when the air is cool, generally below about 50°F. Gas heaters burn natural gas or propane, heat fast in any weather and suit occasional use or spas, but cost more per hour. In most climates, a solar cover is the cheapest first step because most heat leaves through the surface.
Heating extends the swimming season. The best choice depends on climate, how you use the pool and your energy prices.
Side by side
| Heat pump | Gas heater | Solar | |
|---|---|---|---|
| How it heats | Moves heat from air | Burns natural gas or propane | Sun-warmed panels |
| Heating speed | Slow, steady | Fast | Slow, weather-dependent |
| Running cost | Low | High | Near zero |
| Works in cool air | Reduced below about 50°F | Yes | Weak in cool or cloudy weather |
| Efficiency rating | COP (coefficient of performance) | Thermal efficiency percent | Collector area |
| Best for | Keeping a pool warm all season | Quick heats, spas, cold climates | Sunny climates, budget |
Sizing
Heaters are sized in BTUs per hour against pool surface area, desired temperature rise and air temperature. Use the maker’s sizing chart and your pool volume and area. Undersized heat pumps cannot keep up in shoulder seasons.
Start with a cover
Evaporation is the largest source of heat loss. A solar cover reduces evaporation and adds some heat. Use one whatever heater you choose.
Installation
Heat pumps need a 230-volt circuit and open air around the unit. Gas heaters need a properly sized gas line and venting clearances. Both need the pump to deliver enough flow; see variable-speed pumps. Use licensed installers.
Browse heating.
Common questions
Is a heat pump or gas heater cheaper to run?
A heat pump is usually far cheaper per degree of heat, because it moves heat rather than burning fuel.
Do pool heat pumps work in cold weather?
Output drops as air cools. Most work best above about 50 to 55°F; check the maker's rated range.
What size pool heater do I need?
It depends on surface area, desired temperature rise and climate. Makers publish sizing charts by pool area.
Does a pool cover really help?
Yes. Evaporation is the biggest heat loss, so a cover keeps much of the heat you pay for.