Your pool is too cold. Start here.
Four short checks that tell you which of four different problems you have, before you spend anything.
Quick picks
One product per diagnosis. Take the measurements first — the wrong fix for the right problem is money wasted.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | No photo Fixes problem 1 Sun2Solar 1200 Series Crystal Clear Solar Cover Losing heat overnight. The commonest diagnosis and the cheapest fix. | Most pools, most budgets — the default recommendation | |
| 2 | No photo Fixes problem 2 SmartPool SunHeater S601P Solar Heating System Never collecting enough. Adds heat with no running cost. | Adding real heat with no running cost, on a sunny site | |
| 3 | No photo Fixes problem 3 Hayward HeatPro Pool Heat Pump You want a temperature on demand rather than whatever the weather gave you. | Lowest running cost per degree when you want real temperature control | |
| 4 | No photo Fixes the fix Blue Wave Solar Cover Reel If problem 1 is diagnosed and the cover still does not go on, this is the actual blocker. | Any inground pool with a cover you are not using enough |
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Four measurements, ten minutes
“My pool is cold” is four different problems with four different fixes, and buying the wrong one is expensive. These checks tell you which you have.
Check 1: your actual temperature, measured properly
Read a foot down, away from the return jets, ideally after the pump has run for twenty minutes. Not at the surface. After a sunny afternoon the top layer can be several degrees warmer than the water underneath — our arithmetic puts the top foot at around 3°F per hour of sun against 0.66°F for the whole pool. A surface reading flatters the pool and hides the problem.
Compare against DOE’s published ranges: 78 to 80°F for active swimming, 82 to 84°F for recreational use.
Check 2: your overnight drop
Read at dusk. Read again at dawn. The difference is the single most diagnostic number available to you.
Check 3: your daily peak
Read at 6pm on a sunny day. Is the pool ever warm enough, even at its best?
Check 4: the wind
Is the pool in an open, exposed position? DOE puts a 7 mph surface breeze at a 300% increase in energy consumption, which is large enough to be the entire answer on its own.
Now diagnose
| What you found | The problem | What fixes it |
|---|---|---|
| Warm enough at 6pm, several degrees down by dawn | Losing heat overnight | A cover. Cheapest fix, biggest effect. |
| Never warm enough, even at 6pm on a sunny day | Not collecting enough heat | Solar panels or a heater. A cover alone will not solve it. |
| Fine some days, cold on others | You want control, not more heat | A heat pump or gas heater. Weather-dependent heat cannot be scheduled. |
| Exposed site, windy evenings | Convective and evaporative loss | A windbreak, then a cover. |
| Reading 82°F and it still feels cold | Air temperature, or a surface reading | Re-measure properly. Then consider a higher setpoint. |
Problem 1: you are losing it overnight
The commonest diagnosis by a wide margin. Your pool collects perfectly adequate heat during the day and sheds it before morning.
| 20,000 gal x 8.33 x your overnight drop | = BTU lost |
| x 70% (DOE's evaporation share) | = what a cover can address |
| At a 3°F drop | = $9.92 a night on gas |
Buy a cover. It pays for itself in weeks.
And if the cover still would not go on every night, buy a reel with it — an unused cover saves exactly nothing.
Problem 2: you never collect enough
The pool is cold even at its daily peak. A cover will help you keep what you have, but you do not have enough to keep. You need to add heat: solar panels if your site suits them and you can accept the sun’s schedule, or a heater if you cannot.
Problem 3: you want control
The pool is fine on good days and cold on others, and the thing you actually want is a temperature you choose. That is a heater question, and it comes down to speed against running cost.
Problem 4: it is the wind
An exposed pool in a breezy yard can be losing four times what a sheltered one loses. Before buying equipment, try a screen on the prevailing side for a fortnight and re-measure. It is the cheapest experiment on this page.
Problem 5: expectations
If the water genuinely measures 82°F and still feels cold, the water is not the problem. Water pulls heat from skin roughly twenty-five times faster than air does, so the same pool feels warm on a hot still day and cold on a cool breezy evening. Either accept it, or accept the 10 to 30% per degree it costs to go higher.
The order to spend in
- Free: windbreak, pump timing, lower setpoint. Re-measure.
- Cover, around $100. Re-measure.
- Reel, if the cover is not going on. Re-measure.
- Heat, sized to the gap that is left — which by now is much smaller than it looked.
Every step reduces the size of the heater you eventually need, and the heater is 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.
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.
Blue Wave Solar Cover Reel
A reel is the single highest-leverage purchase in this whole category and almost nobody frames it that way. Every DOE saving figure assumes the cover is on the pool when the pool is not in use. A cover that takes two people and five minutes comes off on Friday and goes back on in October. A reel turns that into thirty seconds alone, which is the difference between the savings existing and not.
Best for Any inground pool with a cover you are not using enough
| Type | Wheeled above-ground-style reel for inground and above-ground useThe manufacturer publishes no retrievable specification sheet; figure is as listed at retail. | Retail listing |
|---|---|---|
| Why it matters | Converts a two-person five-minute job into a one-person thirty-second jobOur framing, not a manufacturer claim. The published savings all assume the cover is actually on. | Our arithmetic |
- Turns the cover into something you will genuinely use daily
- Keeps the cover off the ground, which is where covers get damaged
- Wheels, so it moves out of the way
- Costs a real fraction of what the cover itself costs
- Takes up deck space permanently
- Assembly is fiddly on every reel in this category
- How the tube and hardware hold up outdoors across seasons
- Whether the width range covers your pool without a wobble
- Assembly quality and hardware fit
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
Why is my pool so cold?
How do I warm up my pool quickly?
Should I buy a cover or a heater for a cold pool?
- 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
How fast a pool loses heat
Evaporation, radiation, convection and conduction, with the arithmetic on what each night actually costs and a measurement you can take yourself.
Keeping a pool warm overnight
The specific problem of overnight heat loss: what causes it, what each fix is worth, and the order to try them in.
How to heat a pool
The complete walkthrough: what your pool actually needs in BTU, every heating option priced per delivered million BTU, and the order to try them in.
The ideal pool temperature
DOE's recommended ranges for swimming and for lounging, why they differ, and the 10-to-30%-per-degree figure that makes the setpoint the biggest lever you own.
Solar pool covers worth buying
Ranked on the specifications that actually differ between covers — thickness tier and published lifespan — because the only hands-on test in this category found no heating difference at all.
Solar cover vs pool heater
A hundred-dollar cover against a three-thousand-dollar heater, and the measurement that tells you which half of the problem you actually have.