The cheapest way to heat a pool
Two different questions hide inside this one, and they have different answers. Here are both, with the numbers.
Quick picks
Ranked to answer both versions of the question, with the classic trap flagged as a skip.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | No photo Cheapest to buy, best return Sun2Solar 1200 Series Crystal Clear Solar Cover Around a hundred dollars, attacking about 70% of your heat loss. Nothing else is close. | Most pools, most budgets — the default recommendation | |
| 2 | No photo Cheapest way to start Solar Sun Rings Buy two, then two more. Partial coverage, but you can begin for the price of a takeaway. | A pool you would otherwise leave uncovered because the blanket is too much work | |
| 3 | No photo Cheapest to run SmartPool SunHeater S601P Solar Heating System $0.00 per million BTU. There is no cheaper fuel than none. | Adding real heat with no running cost, on a sunny site | |
| 4 | No photo Cheapest controllable heat Hayward HeatPro Pool Heat Pump About a fifth of electric resistance for identical delivered heat. | Lowest running cost per degree when you want real temperature control | |
| — | No photo Cheap to buy, dreadful to run An electric resistance pool heater The trap in this question. Low sticker price, five times the running cost. | 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 September 2, 2026.
Two questions in one
“Cheapest” means two different things and they have different answers, which is why this question gets answered badly so often.
Cheapest to buy: a solar cover, at around a hundred dollars, and nothing else is remotely close.
Cheapest to run: solar panels at $0.00 per million BTU, then a heat pump at about $10.75.
The trap sits between them: an electric resistance heater is cheap to buy and about five times a heat pump’s running cost for identical heat. That is the single most expensive mistake available in this category, and the sticker price is what causes it.
Cheapest to buy: the cover, and it is not close
DOE attributes about 70% of a pool’s heat loss to evaporation, and puts the saving from covering a pool when it is not in use at 50 to 70% of heating cost. There is no other hundred-dollar purchase in this subject that does anything comparable.
| 20,000 gal x 8.33 x 3°F overnight drop | = 499,800 BTU |
| x 70% evaporation share | = 349,860 BTU a night |
| x $10.75 per million BTU (heat pump) | = $3.76 a night |
| x $28.36 per million BTU (natural gas) | = $9.92 a night |
Roughly $564 to $1,488 across a 150-day season, for a cover costing about $100
Payback measured in weeks. Run it on your own overnight drop with the savings calculator.
If a hundred dollars is still too much this month, solar rings are sold individually — you can start with two and add more. And a liquid cover is cheaper again, though nobody publishes a number for what it actually saves.
Free things that work
Genuinely free, and each of them has a published figure behind it:
- Block the wind. DOE’s figure is that a 7 mph surface wind can raise energy consumption by 300%. Moving a temporary pool to a sheltered corner, or putting up a screen on the prevailing side, costs nothing.
- Lower your target by a degree or two. Each degree of setpoint is 10 to 30% of the heating bill, per DOE. 80 instead of 84 is a large saving.
- Run the pump during the warm part of the day. Circulating at 3am moves water through cold pipes and equipment; circulating at 2pm does not.
- Clear shade if you can. Every square foot of surface in shade is collecting nothing.
The no-heater guide works through how far this approach can actually get you, which is further than most people expect and short of what most people want.
Cheapest to run: the delivered-cost table
| Method | Per million BTU | Ratio to heat pump |
|---|---|---|
| Solar panels | $0.00 | — |
| Electric heat pump | $10.75 | 1.0x |
| Natural gas | $28.36 | 2.6x |
| Propane | $35.66 | 3.3x |
| Electric resistance | $53.75 | 5.0x |
From EIA US average residential energy prices and our stated equipment assumptions. Substitute your own rate in the running cost calculator — your utility rate is the input that moves this table most.
A spending order that works at any budget
- $0 — lower the setpoint, block the wind, run the pump in the warm part of the day.
- $25-40 — a couple of solar rings, or a liquid cover.
- $100-200 — a proper cover. The highest-return purchase available.
- $200-400 — a reel, so the cover actually gets used. Skipping this is how covers end up in sheds.
- $500-1,500 — solar panels, if your site has unshaded area. Zero running cost thereafter.
- $2,000+ — a heat pump, sized to the gap that is left after all of the above — which is a smaller and cheaper heater than you would have bought at step one.
The reason this order matters: every step reduces the size of the heater you eventually need, and heaters are the expensive part.
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.
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
| 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 September 2, 2026.
Solar Sun Rings
Floating discs you drop on one at a time instead of wrestling a full blanket, sold individually. That convenience is the whole product, and it comes out of the physics: rings leave gaps, and evaporation carries on through every square foot you did not cover. Expect a fraction of a full cover's effect roughly in proportion to the surface you actually covered, and buy them because you will use them, not because they work better.
Best for A pool you would otherwise leave uncovered because the blanket is too much work
| Coverage | Partial — discs leave gaps between and at the edgesThe gap is not a defect, it is how the product works. It does mean the DOE cover-saving figures do not apply at full strength. | Published standard |
|---|---|---|
| Typical price | About $25 to $35 each, or $140 to $160 or more per setSwim University's published price range, read 2026-09-02. Check the live price before buying. | Retail listing |
- One person can put them on and take them off in a couple of minutes
- No reel, no folding, no dragging anything over the coping
- Buy a few at a time instead of committing to one large purchase
- Partial coverage means partial results — the gaps keep evaporating
- Per square foot of coverage they cost far more than a blanket
- Wind moves them around
- How much surface a given number of rings really covers on your pool shape
- How long the material lasts against a full blanket
- Whether the anchoring holds in a breeze at your site
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 September 2, 2026.
SmartPool SunHeater S601P Solar Heating System
Solar panels that plumb into the return line and heat the water with sunlight rather than fuel, which puts their running cost at zero — the only entry in the whole heating category where that is true. The trade is that you cannot dial in a temperature: the panels deliver what the sun gives them on the day, and on a cloudy week they deliver very little.
Best for Adding real heat with no running cost, on a sunny site
| Type | Roof or ground-mounted solar collector panels, plumbed inlineThe manufacturer publishes no retrievable specification sheet; figure is as listed at retail. | Retail listing |
|---|---|---|
| Running cost | $0 in fuelThe circulation pump is already running for filtration. There is no additional fuel or electricity cost attributable to the heat. | Our arithmetic |
As much as 15 degrees F
Claimed by Bob Vila, describing the S601P. Conditions: Stated as requiring ample sunlight; no time period given. Source
Note the phrasing: with ample sunlight it can boost temperature by as much as 15 degrees. That is a cumulative ceiling reached over days of good sun, not a figure you will see in an afternoon.
- Zero fuel cost, forever — nothing else in this category can say that
- No combustion, no gas line, no additional electrical service
- Panels can be added to as the budget allows
- You get the sun's schedule, not yours
- Needs real unshaded mounting area, and plumbing work to install
- Does nothing on a cold cloudy week, which is when you most want it
- Actual heat output at your latitude, roof pitch and shading
- How the panel material survives a decade of UV and freeze cycles
- Whether the included fittings suit your existing plumbing
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 September 2, 2026.
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 September 2, 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 September 2, 2026.
Questions people actually ask
What is the cheapest way to heat a swimming pool?
Is an electric pool heater cheap?
Can I heat my pool for free?
- 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.
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The complete cost model: what a million BTU costs to deliver with each fuel, what that means per degree and per pool size, and why heat-up cost is not your monthly bill.
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The full payback derivation from one measurement you can take tonight, plus a sensitivity table for people whose pool is nothing like the example.
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.