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Pool Heater FAQ
Quick answer: Most pool heater questions come down to size, speed and running cost. Size depends on surface area and the gap between water and air temperature; speed on volume and heater output; cost on fuel price and efficiency. A nightly cover usually saves more than any equipment upgrade. Professionals must handle gas and 240 V work.
Guides
Sizing questions
How big a pool heater do I need?
Work out two figures and use the larger. The heat-up figure is gallons × 8.34 × degrees of rise, divided by the hours you are prepared to wait. The holding figure is surface area × the water-to-air temperature gap × about 12 BTU per hour per square foot per degree, a long-used planning rule for light wind. Gas heaters are labelled by input, so divide the output you need by efficiency. The pool heater size calculator does both steps.
Why does surface area matter more than depth?
A deep pool holds more water and takes longer to warm the first time, but once warm it loses heat mostly from the surface. Two pools with the same footprint lose roughly the same heat each night, whatever their depth.
Should I size a heat pump differently from a gas heater?
Yes. Heat pumps are rated by output and that output falls as the air cools. Size for your coolest swimming month, and look up the unit's output at that temperature. See the pool heat pump size calculator.
Speed questions
How long does it take to heat a pool?
Roughly, gallons × 8.34 × degrees of rise, divided by the net heat the heater delivers each hour. A typical gas heater may lift a mid-size pool around 1 to 1.5°F per hour on a calm day; a heat pump often manages a fraction of that. Our how long to heat a pool guide and heating time calculator show the maths.
Why does it take longer than the calculator says?
Wind, cold nights, an uncovered surface, a short pump schedule, low gas pressure, scaled heat exchangers or a dirty filter can all slow things down. Our pool heater not heating page lists checks a homeowner can do and the ones that need a technician.
Cost questions
What does it cost to run a pool heater?
Multiply the heat you deliver by your fuel price and divide by efficiency. A gas therm holds 100,000 BTU; a gallon of propane about 91,500 BTU; a heat pump's kWh delivers about 3,412 BTU times its COP. The operating cost calculator takes your own prices.
Is a heat pump always cheaper to run?
Often, in mild air, because a COP of 4 to 6 means each unit of electricity moves several units of heat. In cool weather the COP falls and the gap narrows. Fuel and electricity prices in your area decide the answer.
How much does installation cost?
It varies widely with gas line length, electrical work, permits and pad or plumbing changes. See the installation cost guide for what drives quotes.
Cover and temperature questions
Does a cover really make a difference?
Yes. Evaporation can be the biggest heat loss from an outdoor pool, and a cover that touches the water blocks most of it. Read pool cover heat loss and the solar cover guide.
What temperature should I keep my pool?
Many families choose roughly 78 to 84°F; competitive lap swimmers often prefer cooler water. Each degree warmer adds running cost. The pool temperature guide has ranges and trade-offs.
Equipment questions
Gas or propane?
Same heater type, different fuel. Natural gas needs a utility line; propane needs a tank and deliveries. See natural gas vs propane pool heater.
How long do pool heaters last?
Many last around 7 to 15 years depending on type, water balance, climate and maintenance. Water chemistry is a big factor. See pool heater lifespan.
Can my pool heater also heat my hot tub?
Often yes, through shared plumbing and valves, but a spa's small volume and high target change the maths. See hot tub vs pool heater.
What about above-ground pools?
Smaller heaters and heat pumps are made for them; volume and surface area still rule. See above-ground pool heaters.
Safety questions
Can I install a gas pool heater myself?
No. Gas piping, venting, clearances and combustion air must be handled by a licensed HVAC or pool professional to local code. Never do DIY gas work.
Does a heat pump need special wiring?
Most need a dedicated 240 V circuit with the right breaker, disconnect and bonding, installed by a licensed electrician.
Do pool chemicals affect the heater?
Yes. Low pH and high chlorine can corrode heat exchangers; high calcium can scale them. Keep water balanced and follow chemical product labels.
A quick worked example
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
Assumptions: 15,000 gallons, 420 sq ft, warming from 68°F to 80°F. Energy needed = 15,000 × 8.34 × 12 ≈ 1.5 million BTU. A 200,000 BTU/h gas heater at 84% efficiency with a 20% loss allowance delivers about 134,400 BTU/h net, so roughly 11 hours. Running costs depend on your therm price and how many hours a month the heater fires.
Maintenance questions
Does a pool heater need yearly service?
Most makers recommend an annual check by a qualified technician. For gas units that usually covers burners, the igniter, the flue path, gas pressure and safety switches. For heat pumps it often covers the evaporator coil, refrigerant circuit readings and electrical connections. Homeowners can keep vents and coils clear of leaves, keep the filter clean and log water chemistry each week.
What should I do before winter?
In freezing climates, heaters are typically drained or protected per the maker's winterizing steps, since trapped water can crack a heat exchanger. If you are not sure how, ask your pool service company to include it in the closing visit.
FAQ
Where should a beginner start?
With the pool volume calculator, then the size calculator.
Are your numbers quotes?
No. They are planning estimates for conversations with licensed pros.
Do you cover brand comparisons?
We explain how to compare spec sheets in best pool heaters and Raypak vs Hayward without ranking brands.