Best pool heaters

Start here: Pentair MasterTemp 400K (natural gas). It's the heater most inground-pool owners end up with — 400,000 BTU warms a big pool fast, and Pentair's service network and parts are everywhere. Gas is the right call when you want heat on demand and don't mind the fuel bill.

Who the others suit:

• Pentair MasterTemp 125K — smaller pools and spas up to ~15,000 gallons; same family, less output.
• Raypak 266K — a solid mid-size gas unit with the best owner ratings here; good for medium inground pools.
• Hayward H250 — Hayward loyalists and mid-size pools.
• Pentair ETi 400 — the premium pick: 96% efficiency, titanium exchanger, if gas costs matter long-term.
• Varpoolfaye 120K heat pump — electric, no gas line needed; best for warm climates where it runs efficiently.
• SmartPool S601 solar — cheapest to run, no fuel at all; a supplement for sunny climates, not a fast heater.
• Nirvana NE20 / LTMATE 58K — small above-ground pools and spas.

Skip the tiny 2–3 kW plug-in units: they barely move a real pool's temperature.