Pool heating in Arizona

The honest answer for most Valley homeowners is no — not for the pool itself. Phoenix pools are naturally swimmable from late April through mid-October without any added heat. Where heaters earn their place is twofold: extending swim season into March/April and October/November, and making attached spas usable year-round.

That's the real decision frame. Don't ask 'should I add a heater?' Ask 'will I actually swim in March and November, or do I just want the spa to work in December?' Those two answers point at very different equipment and very different bills.

We routinely build pools with no heater, with gas heaters sized for spa-only use, and with full heat pumps for owners who want a true 9-month season. Each is the right answer for the right family. Wrong answer is over-buying — a $7,500 heat pump on a pool nobody uses past October is the most common Arizona heater regret.

Gas heaters (the Phoenix standard is Raypak) heat your pool fast. A 400,000 BTU heater raises a 14,000-gallon pool's temperature about 1°F per hour. From the moment you fire it up, your pool is swim-ready in 4–6 hours.

Install cost: $3,500–$5,500 installed for the heater itself, plus $500–$2,500 if you need a new gas line run from the meter. Most modern Arizona homes have gas service to the equipment pad as part of the original pool build; older homes or pools added later may need new gas line.

Operating cost in 2026 with Southwest Gas residential rates: roughly $4–$8 per hour of active heating depending on outdoor temperature and target temp. Heating a cold pool from 60°F to 82°F takes 22 hours and burns roughly $90–$170 in gas. Maintaining a heated pool at 82°F through a cool fall week costs $200–$400.

Where gas wins: spa heating (you want it fast, you use it briefly), shoulder-season pool heating for parties and weekend swims, and any scenario where you heat on-demand rather than continuously. Where it loses: anyone trying to maintain a year-round heated pool — operating costs become unbearable quickly.

Solar pool heating uses black polypropylene panels mounted on your roof to capture sun heat and transfer it to your pool water. Once installed, it costs essentially nothing to run — your existing pool pump pushes water through the panels and back to the pool.

Install cost: $4,000–$9,000 depending on panel area, roof access, and integration complexity. You need roughly 50–80% of your pool surface area in panels for meaningful heat gain. South-facing roofs work best. Lifespan: 12–18 years on the panels.

Heat gain: 8–15°F above unheated pool temperature when sun is shining. Solar typically extends the natural swim season by 4–6 weeks on each end — bringing March/early April and mid-October/November into comfortable swim range.

Where solar shines: as a complement to a small gas heater for spa use, on south-facing homes with available roof real estate, and for environmentally-conscious homeowners. Where it falls short: solo (you still need a backup heat source for cloudy days and evenings), small or shaded roofs, and homeowners with HOA roof-mounted-equipment restrictions.

Under-sizing a heater means it never catches up to your desired temperature. Over-sizing wastes money on a unit you never run at full capacity. Standard sizing rules for Arizona pools:

• Gas heater BTU = pool surface area (sq ft) × temperature rise desired (°F) × 12. A 400 sq ft pool wanting 20°F rise needs roughly 96,000 BTU/hour minimum. We round up to next standard size (266k, 333k, 400k, 406k BTU).
• For pools with attached spas, size for spa heating speed (most homeowners want spa from 65°F to 102°F in 30–45 minutes). This usually requires 400k+ BTU regardless of pool size.
• Heat pump sizing: 120k–140k BTU heat pump for pools up to 18,000 gallons. 140k–160k BTU for 18,000–30,000 gallon pools.

We default to a Raypak 406A (406,000 BTU) gas heater on most Arizona builds with a spa. It's enough heater for both jobs.

If you have an attached spa, the spa essentially dictates your heater choice — gas is the only reasonable option for fast spa heating. Heat pumps and solar are far too slow to heat a 600-gallon spa from 65°F to 102°F in the 30–45 minutes most homeowners expect.

A good 400,000 BTU gas heater raises spa temperature roughly 2°F per minute. From cold (65°F) to hot tub (102°F) takes 18–22 minutes. From 'idle' (90°F) to hot tub takes 6 minutes. That speed is what makes spas usable.

Spa-only operating cost: a 30-minute weekly session costs roughly $3–$5 in gas. Heating the spa 3 times a week through fall and winter costs $40–$80 per month. Very affordable for the use you get out of it.

Keep a quality insulated spa cover on between uses. A spa with no cover loses heat fast in 50°F overnight Phoenix winter and your heater runs constantly to maintain. With a cover, the heater only fires up briefly to re-warm before use.