Quick answer: The Pentair MasterTemp 250 (250,000 BTU, around $3,700) is the best natural gas pool heater for most in-ground pools, pairing fast on-demand heat with an 84% thermal-efficiency copper exchanger. Buyers who want to save on upfront cost should look at the Hayward Universal H-Series (around $4,589 for a comparable 250,000 BTU unit), and anyone who wants app control should look at Raypak’s Digital and AVIA natural gas lines, which run the Raymote app over Wi-Fi. All three brands make near-identical natural-gas and propane versions of the same heater — never run a natural-gas-rated unit on propane without a factory conversion kit, since the orifice sizing is different and it’s both a safety hazard and a warranty voider.
| Heater | BTU output | Efficiency | Price | Best for |
|---|---|---|---|---|
| Pentair MasterTemp 250 | 250,000 | 84% (copper) | ~$3,700 | Most in-ground pools, best overall |
| Hayward Universal H-Series (H250FD) | 250,000 | ~84% | ~$4,589 | Value / easier local service |
| Raypak Digital 266K | 266,000 | ~84% | ~$3,200-$3,900 | Budget-friendly natural gas |
| Raypak AVIA 399K | 399,000 | ~84% | ~$4,800 | Large pools, Wi-Fi/app control |
| Pentair MasterTemp 400 | 400,000 | 82% (cupro-nickel HD) | ~$4,789 | Fastest heat-up, large pools |
Why natural gas is still the fastest way to heat a pool
Gas heaters win on speed. A correctly sized natural gas unit raises pool temperature roughly 1-2.5°F per hour, according to sizing data pool professionals use — several times faster than a heat pump’s 0.5-1.5°F per hour, since a gas burner adds heat directly rather than pulling it from ambient air. That makes gas the right call for anyone heating a pool occasionally, warming it up fast before a weekend, or running a spa where the whole point is near-instant hot water. The tradeoff is running cost: gas burns fuel every minute it’s on, while a heat pump’s coefficient of performance means it moves several units of heat per unit of electricity consumed. If running cost matters more than speed, our gas vs heat pump guide breaks down the full cost comparison.
Pentair MasterTemp 250 Natural Gas Pool Heater
- Digital thermostat and electronic ignition standard, no pilot light to relight.
- Sized right for most 15,000-20,000-gallon in-ground pools.
- Cupro-nickel HD version available for salt systems or hard-to-balance water.
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Hayward Universal H-Series Natural Gas Pool Heater
- Lower price than the equivalent MasterTemp size for near-identical output.
- Parts and local service techs are generally easier to find than Pentair's.
- Digital display with diagnostic error codes for faster troubleshooting.
Sizing your gas heater correctly
Undersizing a gas heater is the single biggest mistake buyers make — a unit that’s too small runs constantly and still can’t hold temperature on cold nights. As a starting point, a 10,000-15,000 gallon pool typically needs 150,000-266,000 BTU, a 15,000-20,000 gallon pool needs 250,000-300,000 BTU, and anything above 20,000 gallons should look at the 400,000 BTU tier. Our full sizing chart and BTU calculator walks through the exact formula (gallons x 8.34 x desired temperature rise, divided by hours) if your pool falls between these tiers, and our best pool heater for a 20,000-gallon pool guide picks the exact models for that specific size.
For a deeper look at how Raypak’s Wi-Fi-enabled AVIA and Digital lines compare feature-for-feature, see our best Raypak pool heater breakdown, and for a full head-to-head on the two biggest natural gas brands, see Hayward vs Pentair.
No natural gas line? Go propane instead
Every heater in this roundup is also sold in a propane (LP) version built on the same platform, just with different orifice sizing and a different gas valve regulator. Propane costs more per BTU than piped natural gas in most U.S. markets, but the heater itself performs the same. See our best propane pool heater guide for LP-specific pricing on these same models.
The bottom line
For most in-ground pools, the Pentair MasterTemp 250 is the best natural gas pool heater — fast, efficient, and easy to service. If price is the deciding factor, the Hayward Universal H-Series gets you nearly the same performance for less, and Raypak’s Digital and AVIA lines are worth a look if app control matters to you. Whichever brand you pick, size it correctly using our BTU calculator first — an undersized heater is the most common and most expensive mistake in this category. For the full lineup across every fuel type including heat pumps and solar, see our best pool heater picks.
Sources: Pentair — MasterTemp Spec Sheet, Raypak — Digital and AVIA Product Specifications, U.S. Energy Information Administration — Natural Gas Prices