Your gas heater is twelve years old, the cabinet is rusting at the seams, and you have two questions: what a new one costs, and why last April’s gas bill looked like a car payment. Those are the same question. Pool heater replacement cost is what you pay once. The pool heater running cost is what you pay every month you use the thing, for the next decade. Get the second number wrong and the first barely matters, which is why our pool repairs and upgrades work starts with how you actually heat, not with whatever is on sale.

So, do pool heaters use a lot of electricity? Some of them use a startling amount. Some use almost none and burn gas instead. The type you pick decides which utility gets the money, and how much.

What a heat pump actually draws

Hayward’s HeatPro sell sheet lists the HP21404T, its 140,000 BTU model, at 7.2 kW with a COP of 5.7 when the air is 80°F and humid (5.5 at a drier 63% humidity). COP is heat out divided by electricity in, so 5.7 means you get 5.7 units of heat for every unit you pay SCE for. The Department of Energy puts heat pump COPs at 3.0 to 7.0 generally.

Now drop the air to 50°F. The same sheet shows output falling to 85,000 BTU and COP to 4.0. Pentair’s UltraTemp brochure tells the same story: the UltraTemp 140 makes 143,000 BTU at a COP of 5.8 in warm air and 88,000 BTU at 4.0 in cool air. Pentair doesn’t print a kW figure, but the arithmetic (BTU divided by 3,412, divided by COP) puts it at about 7.2 kW warm and 6.4 kW cool.

Read those two together. The power draw barely moves when it gets cold. The heat coming out drops by about 40%. You pay nearly the same per hour for a lot less warm water, which is the part nobody mentions at the store.

SCE’s June 2026 rate advisory puts the average residential rate at 34.4 cents a kWh, a tenth of a cent under January. At 34.4 cents, 7.2 kW is $2.48 an hour. Run it eight hours a day for a month and that’s about 1,730 kWh, or roughly $600. For scale, SCE’s own advisory uses a 500 kWh a month household as its typical customer. A busy heat pump can use three times what your whole house does.

Gas heaters burn therms, not kilowatts

A gas heater’s BTU rating is input, the fuel it burns, and a therm is 100,000 BTU. So a 400,000 BTU heater burns 4 therms every hour the burner is lit. SoCalGas’s January 2026 rate alert put the residential rate at $2.08 a therm, which makes that hour cost $8.32.

Not all of it reaches the water. Pentair’s 2024 gas heater brochure lists the MasterTemp at 84% thermal efficiency and the ETi 400 at 96%. An 84% heater puts about 336,000 BTU an hour into the pool. That’s the gas heater’s whole argument: it costs more per hour and gets the job done in a fraction of the hours.

The electricity a gas heater uses (controls, igniter, a blower on forced draft models) is small next to the gas. And the gas price moves. SoCalGas’s pricing page says the commodity part of the rate changes monthly, and it set September 2026’s at 41.385 cents a therm, about 14.4% above September 2025. We already ran the per-BTU comparison in our post on repairing or replacing a pool heater. Short version: at our rates the heat pump wins, by less than the brochures suggest.

Electric resistance heaters are the expensive ones

These are the heaters that deserve the “uses a lot of electricity” reputation. A resistance heater is a big version of the element in your water heater. Raypak’s E3T page lists 100% thermal efficiency, which sounds wonderful until you remember a heat pump runs at 400 to 570%.

Raypak’s largest single-phase E3T, the 0027, is rated 92,000 BTU an hour, which works out to 27 kW. At 34.4 cents that’s $9.29 an hour for 92,000 BTU. The Hayward heat pump above makes 140,000 BTU for $2.48. Same electric company, same meter, roughly a quarter of the cost for more heat.

The Department of Energy’s heat pump guidance runs the same comparison: swap a resistance heater costing $1,000 a year for a heat pump with a COP of 5.0 and you save about $800 a year.

On a small spa that heats for an hour now and then, fine. On a pool, don’t buy one.

Monthly running cost for a typical pool

Now a real bill. The Department of Energy’s gas pool heater guide publishes annual heating costs for a 1,000 square foot pool in Los Angeles, heated May 1 through October 31, with an 80% efficient gas heater at $1.09 a therm. It doesn’t list Ventura County. Los Angeles is the nearest city in the table.

We took those figures, scaled them to a 16 by 32 foot pool (512 square feet of surface), repriced the gas at SoCalGas’s $2.08 and converted the same heat to electricity at SCE’s 34.4 cents. It’s a model, not a meter reading. Wind, shade and how often you swim will move yours.

Monthly figures are the six-month season divided by six. We used a COP of 5.0 for the warm months and 4.0 for cool air, both inside the spec sheet ratings. An 84% heater like the MasterTemp would come in about 5% under the gas row.

National guides quote much friendlier numbers. Angi’s 2026 data puts heat pump running costs at $120 to $200 a month and gas at $200 to $400. HomeGuide says $50 to $150 for a heat pump. Those guides don’t pay SCE’s rates. If your bill lands near them, you are covering the pool or not heating it much, both of which are fine.

How season and target temperature change the bill

Target temperature is the dial people underestimate. In the DOE’s Los Angeles numbers, going from 78°F to 80°F adds about 27% to the season’s cost. Going from 80°F to 82°F adds another 22%. Call it a quarter more for every two degrees.

The cover column is the other dial. At 82°F, the DOE’s covered Los Angeles figure is 84% below the uncovered one. Covers get their own post, so that’s all we’ll say, except that it’s the biggest number on this page.

Season matters because of the heat pump curve. The DOE’s season runs May through October. Want the pool warm in March, April or November and you’re heating when the nights are cool. The DOE says heat pumps work efficiently only above about 45 to 50°F air, and both spec sheets show COP sliding to 4.0 at 50°F. Spring heating costs more per degree than summer heating, on any heat pump.

Pool heater replacement cost by type

Angi’s 2026 data puts the average pool heater installation at $3,094, with most homeowners paying $1,864 to $4,348. By type, installed: gas $1,500 to $6,000, heat pump $2,500 to $7,500, electric resistance $1,000 to $6,000. HomeGuide’s 2026 ranges run a little lower: gas $1,500 to $4,500, heat pump $2,000 to $6,000, electric $1,200 to $6,000.

The extras are where quotes jump. Angi lists a new gas line at $500 to $2,000 and a new electrical circuit at $250 to $2,100. Swapping gas for gas usually needs neither. Switching from gas to a heat pump usually needs the circuit, because Hayward’s sheet calls for 42 minimum circuit amps on the 140,000 BTU model.

Then there’s how long you get to use it. The DOE says gas pool heaters typically last five or more years and heat pumps 10 or more.

Total cost: which replacement pays for itself

Put the two halves together: pool heater replacement cost on one side, the running bill on the other. Say the heat pump costs $1,000 more installed than a gas heater, which is the gap between the bottoms of Angi’s two ranges.

Heat an uncovered pool to 80°F all season and, from the table, the heat pump saves about $700 a season. It pays back the difference in under two years. Easy call.

Cover that same pool and the savings shrink to about $90 a season. Now the payback is eleven years. That’s longer than the DOE’s floor on heat pump life.

So here’s where we land. Heat the pool steadily from spring to fall: heat pump, and put it on a midday schedule. Heat a spa, or the pool for a weekend here and there: gas, because a 140,000 BTU heat pump moves a 20,000 gallon pool less than a degree an hour and can’t catch up by Saturday. Electric resistance: small spa or nothing.

One more line on the bill: the filter pump runs whenever the heater does. If yours is an old single-speed, California’s variable speed pump rule is worth reading before you add heating hours.

Questions we get at the pad

Does a gas pool heater use electricity? A little, for the board, igniter and blower. The gas is the bill.

Will a heat pump double my electric bill? It can. Eight hours a day at 7.2 kW is about 1,730 kWh a month. SCE’s typical customer uses 500.

Is propane cheaper? Rarely. Angi puts propane heating at $200 to $850 a month, the widest range on its list.

Can I cut the bill without replacing anything? Yes. Drop the setpoint two degrees, run the heater midday, cover the pool. That’s the whole list. More in our pool FAQs.

Pull two bills before you price a heater

Before anyone quotes a pool heater replacement cost, find last April’s SCE and SoCalGas bills and write down the temperature you actually keep the pool at and which months you heat. That tells you, and us, whether you’re a heat pump household or a gas one.

Then send us the details through the site: those numbers, plus the brand, BTU rating and model off the old heater’s data plate. We service Pentair, Jandy, Zodiac, Hayward and Sta-Rite equipment, and we’ll tell you which replacement fits how you swim. Call (805) 586-2055 and we’ll get a tech out to the pad.