A pool heat pump is the better investment for most people.

Unless you need to heat the pool fast or live somewhere that rarely hits 50°F, get the heat pump.

Heat pumps are slower but way cheaper to run. They pull heat from the air, so you’re paying for electricity to move heat, not create it. Over a season, you’ll spend maybe a third of what you would on gas. They also last longer — 10–15 years vs 5–10 for a gas heater. The catch: they take hours to raise the temperature, so you can’t decide at 9 AM that you want a warm pool by noon.

Gas heaters win on speed and cold weather. If you want to heat the pool for a single weekend party, or you live where winter nights drop below 50°F and you still want to swim, gas works better. They also cost less upfront — usually $1,500–$2,500 vs $3,000–$5,000 for a decent heat pump. But you’ll pay that difference back in fuel cost in a couple years if you use the pool regularly.

Bottom line: heat pump for regular swimming, gas for occasional use or cold climates. I’d go heat pump unless you have a specific reason not to.