Electric pool heaters
The same phrase covers two machines whose running costs differ by five times. Everything depends on which one you are looking at.
Quick picks
Both kinds of electric heater are on this list on purpose. The skip entry is not a bad product, it is the right product for a spa and the wrong one for a pool.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 |  The electric heater to buy Hayward HeatPro Pool Heat Pump A heat pump moves heat instead of making it — about $10.75 per million BTU delivered. | Lowest running cost per degree when you want real temperature control | |
| 2 |  For a smaller pool FibroPool FH255 55,000 BTU Pool Heat Pump A published COP of 5.92 on a machine sized for pools a full-size heat pump would be wasted on. | A smaller pool where a full-size heat pump is more machine than the water needs | |
| 3 |  Buy this first, whichever you choose Sun2Solar 1200 Series Crystal Clear Solar Cover The heater you need gets smaller once the pool stops losing heat overnight. | Most pools, most budgets — the default recommendation | |
| — | No photo The other electric heater An electric resistance pool heater About $53.75 per million BTU — five times the heat pump, on identical electricity. | Spas and very small above-ground pools only |
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
The phrase means two different machines
“Electric pool heater” is a search term that returns two fundamentally different products, and the listings rarely make the difference obvious. One of them is the cheapest way to heat a pool that has a thermostat. The other is the most expensive way to heat water that exists. They plug into the same electricity.
- A heat pump does not make heat. It extracts heat from outdoor air and moves it into the water, the way an air conditioner moves heat out of a room. Because it is moving energy rather than creating it, it delivers several units of heat for every unit of electricity it draws.
- A resistance heater passes current through an element, exactly like a kettle. It converts electricity into heat at essentially one to one. There is no efficiency to argue about and no way to improve it — the physics is settled.
That difference is worth this much:
| Machine | Per million BTU delivered | 20,000 gal, +10°F |
|---|---|---|
| Heat pump (assumed COP 5.0) | $10.75 | $17.91 |
| Resistance element (COP 1.0) | $53.75 | $89.55 |
Both computed from the same US average residential electricity price, 18.34 cents per kWh (EIA, June 2026). The entire difference is the machine. Substitute your own rate here.
How to tell which one a listing is selling
The listings do not always say, and the vocabulary is unhelpful — both get described as electric, both get described as efficient. Four tells that work:
- Size and shape. A heat pump is a large box with a fan on top and a finned coil down the sides, and it weighs a great deal. A resistance heater is a small in-line cylinder or a compact wall unit.
- The letters COP. Only a heat pump has a coefficient of performance worth quoting, because only a heat pump has one above 1. If a listing advertises a COP of 5 or so, it is a heat pump.
- kW versus BTU. Resistance heaters are usually rated in kilowatts, heat pumps in BTU per hour. A 3 kW rating is a resistance element; a 140,000 BTU rating is a heat pump.
- The pool size claimed. Resistance units are usually rated for a few thousand gallons at most. Anything claiming a full-size inground pool is a heat pump.
When a resistance heater is genuinely right
This is not a bad product, it is a misapplied one. The running-cost penalty scales with the volume of water, so on a small enough body of water it stops mattering:
- A spa or hot tub. A few hundred gallons, heated occasionally, where the machine cost and the install simplicity dominate.
- A very small above-ground pool, where the total energy is small and the alternative is a project rather than a purchase.
- Anywhere a heat pump cannot physically go — no clearance, no pad, nowhere to put a box that needs unobstructed airflow.
Outside those cases the arithmetic is brutal and it does not improve with use. The above-ground page works through where the line actually falls.
What a heat pump asks of you
Choosing the right machine is not the end of it. A heat pump makes three demands that catch people out after the purchase:
A dedicated circuit. A full-size heat pump draws serious current on 240 V and needs its own breaker and its own run. Small units like the FibroPool still want a dedicated 240 V circuit. Budget an electrician unless you already have a suitable spare.
Air, and lots of it. The machine is pulling heat out of the air passing through it, so it needs clearance on all sides and above. Boxed into a corner it recirculates its own chilled exhaust and its performance falls away.
Patience. This is the slow option. A 140,000 BTU heat pump moves 20,000 gallons about ten degrees in roughly twelve hours, against about six for a large gas heater. The heat pump against gas is the comparison that settles whether that matters to you.
If what brought you here was a search for the most efficient heater, this is the category where the word misleads most: the resistance element is the one rated nearest 100%, and it is the dearest to run. Efficiency ranked on one honest scale works that through.
Sizing an electric heater
Heat pumps are rated by heat output, which makes them the easy case: a 140,000 BTU heat pump delivers 140,000 BTU an hour into the water. Gas heaters are rated by fuel input and deliver about 82% of it, so the two numbers on two listings are not comparable. This trips up more buyers than any other single thing in the category, and the sizing guide runs the conversion both ways.
To size from the water rather than a rule of thumb: gallons times 8.33 times the degrees you want gives the energy, and dividing that by the hours you are willing to wait gives the BTU per hour you need.
| 20,000 x 8.33 x 10°F | = 1,666,000 BTU |
| Willing to wait 12 hours | = 138,833 BTU/hr |
| So: a 140,000 BTU heat pump | about right |
Ideal figures that ignore the heat the pool loses while you heat it, which on a cool night is not small. Size up rather than down if you are between two machines — oversizing costs purchase price, undersizing costs you the set point.
Do this before buying either one
Every figure above is the cost of replacing heat. About 70% of what you are replacing left through evaporation, which is a loss a cover addresses and no heater does.
Measure your pool at dusk and again at dawn. A drop of several degrees means a large part of your problem is loss rather than supply, and a cover bought before the heater makes the heater you eventually buy smaller, cheaper to run, and quicker to get there. If the pool holds steady overnight and is still cold, your problem genuinely is supply and an electric heat pump is the cheapest controllable answer to it.
Every pick, in detail
What each one publishes, what is good and bad about it, and — the section this category usually omits — what we could not judge without owning one.
Hayward HeatPro Pool Heat Pump
If you are heating a pool with electricity, this is the shape of machine to do it with. A heat pump moves heat instead of making it, and at the assumptions we publish it delivers a million BTU into the water for about a fifth of what an electric resistance heater costs to deliver the same. It is slower than gas and it fades as the air gets colder, which is exactly when you want it — that trade is the whole decision.
Best for Lowest running cost per degree when you want real temperature control
| Type | Air-source heat pumpThe manufacturer publishes no retrievable specification sheet; figure is as listed at retail. | Retail listing |
|---|---|---|
| Rating convention | Rated by BTU/hr OUTPUTThis is the trap in the category. Gas heaters are rated by fuel INPUT, heat pumps by heat OUTPUT. A 140,000 BTU heat pump and a 140,000 BTU gas heater do not deliver the same heat. | Published standard |
| Cost per million BTU delivered | About $10.75 at our published assumptionsUS average residential electricity at 18.34 cents/kWh (EIA, June 2026) and an assumed COP of 5.0. Both are substitutable on our running-cost calculator. | Our arithmetic |
- Cheapest running cost per delivered BTU of any controllable heater
- No gas line, no combustion, no flue
- Holds a set temperature rather than depending on the weather
- Slow — expect most of a day to move a full-size pool ten degrees
- Efficiency falls with air temperature, so it is weakest in the shoulder season
- High purchase price against a gas heater of comparable output
- The COP this specific unit achieves at your conditions
- Compressor and control-board longevity
- Noise at the distance your deck actually sits from it
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
FibroPool FH255 55,000 BTU Pool Heat Pump
The heat pump worth looking at when a full-size one is more machine than the pool needs. FibroPool publishes 55,000 BTU/hr of output and a rated COP of 5.92, which is above the 5.0 we assume for heat pumps generally — so on the pool sizes the manufacturer actually names, the running cost lands below the category figure. The catch is the other side of the same number: 55,000 BTU/hr is not much heat, and on a pool larger than FibroPool lists it will run all day and never catch up.
Best for A smaller pool where a full-size heat pump is more machine than the water needs
| Rated output | 55,000 BTU/hrPublished as OUTPUT, which is the heat-pump convention. It is not comparable with a gas heater's input rating. | Manufacturer |
|---|---|---|
| Pool sizes the manufacturer names | Above-ground up to 21 ft round or 15 x 30 ft oval; inground up to 10,000 gallons | Manufacturer |
| Supply | 240 V | Manufacturer |
| Rated COP | 5.92FibroPool words this as 5.92 times the heat for every dollar of electricity. The conditions it was rated under are not published, and a heat pump's COP falls as the air cools, so read it as a best case rather than a season average. | Manufacturer |
| Cost per million BTU delivered | About $9.08 at the published COPUS average residential electricity at 18.34 cents/kWh (EIA, June 2026) divided by the published COP of 5.92. At the more conservative COP of 5.0 we use across the site it comes out at about $10.75. | Our arithmetic |
- A published COP of 5.92, above the 5.0 we assume for the category
- All electric — no gas line, no flue, no combustion air to arrange
- Sized and priced for pools that a full-size heat pump is wasted on
- 55,000 BTU/hr is modest: about 30 hours to lift 20,000 gallons ten degrees
- Wants a dedicated 240 V circuit, which is an electrician's visit if you do not have one
- Like every heat pump, it fades as the air cools — the shoulder season you bought it for
- The COP this unit reaches at your air temperature and humidity
- Compressor and control-board life, which decides whether a cheaper heat pump is a bargain
- How loud it is at the distance your deck actually sits from it
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
Sun2Solar 1200 Series Crystal Clear Solar Cover
The value pick, and the one whose logic actually holds up. A clear cover transmits more sunlight into the body of the pool instead of absorbing it at the surface, and 12 mil is the point where lifespan stops being the limiting factor. Bob Vila measured this and the 16-mil blue at the same 4 to 5 degrees in an hour, so you are paying less for the same measured result and giving up some years of service life.
Best for Most pools, most budgets — the default recommendation
| Price shown for | 20 x 40 ft rectangleThis product is sold in several sizes on one listing. The live price and photograph on this page are the ones Amazon returns for this variant; other sizes are priced separately. | Retail listing |
|---|---|---|
| Thickness | 12 milThe manufacturer publishes no retrievable specification sheet; figure is as listed at retail. | Retail listing |
| Color | Clear | Retail listing |
| Stated lifespan | 3 to 4 years for the 12-mil clear tierSwim University's published figure for 12-mil clear covers generally. | Retail listing |
| Bubble side | Bubbles face the water | Published standard |
4 to 5 degrees F in one hour
Claimed by Bob Vila, measured across all covers in their group. Conditions: One hour under 2pm sun on 89 to 92 degree F days. Source
- Clear transmits more light into the water instead of stopping it at the surface
- 12 mil is the sweet spot: real service life without 16-mil bulk
- Cheaper than the 16-mil tier with no measured heating penalty
- Shorter published lifespan tier than 16 mil
- A clear cover shows algae and debris more obviously, which some people dislike
- Whether clear genuinely outlasts or under-lasts blue in the same thickness
- Real-world tear resistance at a pool with rough edges
- How much the clear material clouds over a season of UV
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
An electric resistance pool heater
Skip it for a full-size pool, and the arithmetic is not close. At the same electricity price, a resistance heater costs about five times what a heat pump costs to deliver the same heat, because it makes heat instead of moving it. It has a legitimate niche on a small above-ground pool or a spa where the volume is tiny and the install is a plug. On 20,000 gallons it is the most expensive way to heat water that exists.
Best for Spas and very small above-ground pools only
| Cost per million BTU delivered | About $53.75 at our published assumptionsUS average residential electricity at 18.34 cents/kWh (EIA, June 2026) at a coefficient of performance of 1.0. Compare with about $10.75 for a heat pump on the same electricity. | Our arithmetic |
|---|---|---|
| Efficiency | About 1:1 — no efficiency to argue about | Published standard |
- Cheap to buy and often just plugs in
- Genuinely sensible on a spa or a very small pool
- About five times a heat pump's running cost for identical heat
- Draws serious current, which frequently means an electrical upgrade
- On a full-size pool the running cost is punishing
- Element life in your water chemistry
- Whether your existing circuit can carry it
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
Questions people actually ask
Are electric pool heaters expensive to run?
Is a pool heat pump an electric heater?
Can I run a pool heater on a normal outlet?
How long does an electric pool heater take to heat a pool?
Does a pool heat pump work in cold weather?
- Average retail price of electricity to US residential customers: 18.34 cents/kWh, June 2026U.S. Energy Information Administration · read 2026-09-02
- US residential natural gas price: $24.09 per thousand cubic feet, June 2026U.S. Energy Information Administration · read 2026-09-02
- US residential propane price: $2.674 per gallon, week ending 30 March 2026U.S. Energy Information Administration · read 2026-09-02
- Energy content conversion factors: 3,412 BTU per kWh, 1,036 BTU per cubic foot of natural gas, 91,452 BTU per gallon of propaneU.S. Energy Information Administration · read 2026-09-02
- U.S. Department of Energy pool-energy figures (evaporation share, BTU per pound evaporated, cover savings, recommended temperatures, wind effect)Recreonics, reproducing and attributing the U.S. Department of Energy · read 2026-09-02
- Pool heater roundup: the 8.33 BTU per gallon per °F figure, attributed on the page to Alicia Toedter of Leslie'sBob Vila · read 2026-09-02
Every URL above was fetched and returned content on the date shown. Where a figure is ours rather than somebody else’s, the arithmetic is on the page and on the methodology page. If you find an error in it, we would genuinely like to know.
Read next
Heat pumps for above-ground pools
18,000 to 55,000 BTU heat pumps for above-ground pools, including 110V plug-in units. Ranked on published output and warranty, with the hours-to-temperature arithmetic.
AquaCal HeatWave SuperQuiet review
AquaCal's SuperQuiet line on the record: a published COP of 5.7 at a summer test condition, a titanium exchanger, a narrow flow window, and less heat per hour than the two full-size rivals this site already ranks.
Pool heat pumps worth buying
Full-size and small heat pumps ranked on published output, exchanger material and what the manufacturer will actually say about efficiency. With the sizing math for your pool.
The most efficient pool heaters
Efficiency ranked properly: COP against thermal efficiency, why a heater rated 100% is the worst buy, what the 2028 federal standard changes, and the picks that come out on top.
Which pool heater to buy
Every type of pool heater ranked on what it costs to deliver a million BTU into the water, how many hours it needs to do it, and what the install actually involves.
Heat pump vs gas pool heater
The two options priced per delivered BTU and timed on the same pool, with the one question that decides which trade suits you.
What a pool heat pump costs to run
The heat pump running-cost derivation, what happens to it in cold air, and the two inputs that change the answer more than anything else.
What size pool heater do I need?
How to size a heater from your pool's actual energy requirement, the input-versus-output rating trap, and why the answer gets smaller once you own a cover.
Heaters for above-ground pools
Why a small pool is much cheaper to heat, which options make sense at that scale, and the one place an electric resistance heater is genuinely defensible.
Can you heat a pool with a water heater?
Why a domestic or tankless water heater cannot do a pool heater's job even when its BTU rating looks adequate: the minimum flow rate, the connection size and the water it was built for.