Heating a pool without a heater
A real strategy rather than a consolation prize — with a limit that is worth knowing before you commit to it.
Quick picks
Everything on this list either keeps heat or collects it without a fuel bill.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | No photo The one that does most of the work Sun2Solar 1200 Series Crystal Clear Solar Cover About 70% of your loss is evaporation, and this is what stops it. | Most pools, most budgets — the default recommendation | |
| 2 | No photo What makes it stick Blue Wave Solar Cover Reel The strategy depends on the cover going on every night. This is what makes that happen. | Any inground pool with a cover you are not using enough | |
| 3 | No photo Adding heat without a heater bill SmartPool SunHeater S601P Solar Heating System Technically a heater, practically free to run. The natural next step. | Adding real heat with no running cost, on a sunny site | |
| 4 | No photo When a blanket will not work HeatSavr Liquid Solar Cover For pools where no cover fits or nowhere to store one. | Odd-shaped pools and anyone who will never use a blanket |
#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.
Reframe the problem first
“Heating without a heater” usually turns out to mean losing less rather than gaining more, and that is fortunate, because the loss side is where the leverage is.
The Department of Energy attributes about 70% of a pool’s heat loss to evaporation. A pool that drops 3°F overnight is shedding around 500,000 BTU, roughly 350,000 of it through a mechanism a sheet of plastic largely stops. You do not have to add that heat if you do not lose it.
What actually works, with the figure behind each
1. A cover, used every night
The single most effective thing available. DOE puts the heating-cost saving from covering a pool when it is not in use at 50 to 70%. Nothing else on this page is in that territory.
The catch is compliance, not equipment. A reel is what turns a good intention into a nightly habit, and without one a full-size cover stops going on within weeks.
2. Block the wind
DOE’s figure here is startling and under-used: a 7 mph wind across the surface can increase energy consumption by 300%. Seven miles an hour is a light breeze — a flag stirring.
If your pool sits in an open yard, a hedge, a fence or even a temporary screen on the prevailing side is doing more thermal work than most equipment upgrades, for a fraction of the price. This is the most under-rated item in the whole subject.
3. Lower your target temperature
Each additional degree of setpoint costs 10 to 30% more, per DOE. DOE’s own recommendation is 78 to 80°F for active swimming and 82 to 84°F for recreational use — and a lot of people are heating to the recreational number for a pool that is used for swimming. What to aim for.
4. Run the pump in the warm part of the day
Circulation at 3am pushes water through cold pipes, a cold filter and cold equipment, and returns it to a pool that is radiating to a clear night sky. The same run at 2pm does the opposite. Same electricity, same filtration, better thermal outcome.
5. Clear the shade
Every square foot of surface in shade at midday is collecting nothing. Overhanging branches are worth a look, and they are dropping debris into the pool anyway.
6. Solar panels — technically a heater, practically free
If you will allow one purchase, solar collectors are the natural extension of this strategy: no fuel, no gas line, no additional electrical service, and your existing pump does the work. A home-built version is genuinely feasible here in a way it is not for any other heating technology.
Where this approach runs out
Here is the honest limit, because a page that only lists upsides is not much use.
How to tell whether it is working
Measure, do not guess. Read the pool temperature at dusk and again at dawn, a foot down and away from the returns, on a still clear night. That difference is your overnight loss and it is the number every calculation on this site starts from.
Do it once uncovered and once covered and you will have your own measurement of what the cover is doing for your pool — which is worth more than any number we or anyone else can publish. Turn it into dollars here.
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.
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.
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.
HeatSavr Liquid Solar Cover
A monolayer chemical that spreads a molecule-thick film across the surface to slow evaporation. It is the only option here that does not require you to physically cover anything, which is exactly why people buy it — and it is also the reason to be careful with the claims: a film that thin is disrupted by swimmers, wind and the return jets, and it is doing nothing for the hours after that until it re-spreads.
Best for Odd-shaped pools and anyone who will never use a blanket
| How it works | Self-spreading monolayer that slows surface evaporation | Published standard |
|---|---|---|
| Typical price | About $10 to $30 or moreSwim University's published range for liquid covers generally, read 2026-09-02. | Retail listing |
| Effect on daytime gain | None to speak ofA monolayer is optically negligible. Any benefit is on the evaporation side, which is the overnight-retention mechanism, not daytime gain. | Our arithmetic |
- Works on any pool shape, including the ones no blanket fits
- Nothing to store, fold, drag or trip over
- Cheap enough to try
- Disrupted by swimming, wind and circulation, and takes time to re-form
- Nothing published that would let you quantify what it actually saves
- Does not warm the pool during the day the way a physical cover can
- How much evaporation it actually suppresses on a real pool
- How quickly the film re-forms after use
- Whether dosing frequency in practice matches the label
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
How can I heat my pool without a heater?
How much warmer can I get my pool without a heater?
Do black garbage bags heat a pool?
- 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
- U.S. Department of Energy, Energy Saver: Swimming Pool Covers (archived — the live page now returns 404)U.S. Department of Energy via the Internet Archive · read 2026-09-02
- Average retail price of electricity to US residential customers: 18.34 cents/kWh, June 2026U.S. Energy Information Administration · 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
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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.
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.
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Building your own solar pool heater
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