Do solar pool covers work?
One buying guide says 4 degrees. Another says 15. They are both telling the truth, and here is why — with the arithmetic.
Quick picks
Two picks placed after the explanation rather than before it, because the recommendation only makes sense once you know which of the three numbers you are buying.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | No photo If you are convinced Sun2Solar 1200 Series Crystal Clear Solar Cover The 12-mil clear cover we would buy, once you know what to expect from it. | Most pools, most budgets — the default recommendation | |
| 2 | No photo The bit that makes it work Blue Wave Solar Cover Reel None of this happens if the cover does not go on. | Any inground pool with a cover you are not using enough |
#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.
The contradiction
Search for whether solar covers work and you will be told, by pages that all rank on the first screen, that a cover will raise your pool by 4 degrees, or 10 to 15 degrees, or “up to 15”, or 5 to 8 degrees per twelve hours. That is a three- to four-fold spread, and not one of those pages reconciles itself with any of the others.
Some of that is marketing repetition. But the core of it is not dishonesty at all — it is three genuinely different physical quantities being reported under one label. Once you separate them, every one of those numbers turns out to be approximately right about something.
| Quantity | What it measures | Where the claims land |
|---|---|---|
| Daytime solar gain | How far the water rises across one sunny afternoon | Bob Vila's measured 4-5°F |
| Overnight retention | How much heat is NOT lost between dusk and dawn | The '5-8°F per 12 hours' claims |
| Cumulative equilibrium | Where the pool settles after days of continuous use | The 10-15°F claims |
Every temperature claim on this site names which of these three it is. It is the single most useful discipline in the subject and almost nobody applies it.
Now the interesting part
Two of the most credible pages in this category publish figures that look flatly incompatible even after you sort them into buckets, and working out why turns out to be genuinely informative.
Bob Vila states its method, which almost nobody does: each cover sat on the water for an hour in mid-afternoon sun, and “each of the pool covers increased the temperature 4 to 5 degrees Fahrenheit in 2 pm sun on 89- to 92-degree Fahrenheit days.” That is roughly 4.5°F per hour.
Swim University publishes, on the same subject, that “this energy will heat the pool by about 0.7°F per hour under the noontime sun.”
Those differ by a factor of six. They cannot both describe the same water. So we worked out what the sun can actually deliver.
| 1,360 W/m² at the top of the atmosphere | NASA |
| x 48% absorbed at the surface | NASA |
| = about 653 W/m² under a clear midday sky | |
| 16 x 32 ft pool = 512 sq ft = 47.6 m² | |
| 653 x 47.6 = 31,063 W | |
| x 3.412 BTU/hr per watt = 105,987 BTU/hr | |
| ÷ (19,149 gal x 8.33 BTU/gal/°F) |
About 0.66°F per hour
Our arithmetic, from NASA's published energy budget and the standard water constants. Note how closely it lands on Swim University's independently published 0.7°F per hour — two different routes to the same answer is a good sign that the answer is right.
So the physics says a full-size pool cannot gain 4 to 5 degrees in an hour of sunshine. The energy is not there. Even on a small above-ground pool the ceiling is around 1 degree an hour.
Which raises the obvious question: what was Bob Vila’s thermometer reading?
The most likely answer, and why it matters to you
Stratification. Under a solar cover, the water in the top few inches is absorbing energy into a tiny fraction of the pool’s mass, with nothing mixing it downward. That thin layer heats dramatically faster than the body of water beneath it.
| 105,987 BTU/hr | as above |
| Top 12 inches of a 512 sq ft pool | 512 ft³ = 3,830 gallons |
| ÷ (3,830 x 8.33) |
About 3.3°F per hour — and into the top 6 inches, about 6.6°F per hour
Which brackets the 4-to-5°F figure neatly. We cannot prove this is what happened, and we are not accusing anyone of anything: it is the explanation that fits both published numbers without either of them being wrong.
This is not a technicality. It has a direct practical consequence for anybody who owns a cover:
So: do they work?
Yes, and mostly not in the way they are marketed. Here is the honest version:
- As a daytime heater, a cover is modest. The sun delivers what the sun delivers, and a cover’s contribution to daytime gain is real but bounded by the energy arriving.
- As an overnight blanket, a cover is the most cost-effective thing you can buy for a pool. DOE attributes about 70% of a pool’s heat loss to evaporation, and a cover attacks exactly that. On a 20,000-gallon pool dropping 3°F overnight, that is around 350,000 BTU a night it is defending — worth $3.76 with a heat pump, $9.92 with natural gas.
- Over a season, those two combine into the 10-to-15-degree claims, which is a cumulative equilibrium figure, not something you will watch happen in an afternoon.
DOE’s own published figure is that covering a pool when it is not in use saves 50 to 70% of heating cost. That is the number to plan around, and it is about money rather than degrees — which is a better way to think about a cover anyway.
If you want it in dollars for your own pool, the savings calculator takes your overnight drop and works it through.
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.
Questions people actually ask
How many degrees will a solar cover raise my pool?
Why do different websites give completely different numbers?
Why did my pool feel warm when I pulled the cover off and then feel cold?
Is a solar cover worth buying, then?
- Earth's energy budget: 1,360 W/m² of solar energy at the top of the atmosphere, about 48% absorbed at the surfaceNASA Earth Observatory · read 2026-09-02
- Hands-on solar cover comparison: 4 to 5°F measured in one hour of 2pm sun on 89–92°F days, with the method statedBob Vila · read 2026-09-02
- Solar cover guide: 0.7°F per hour under noontime sun, 10–15°F held, and published lifespan tiers by thicknessSwim University · 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
- 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
- Water density: 62.424 pounds per cubic foot at 39.2°FU.S. Geological Survey, Water Science School · 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 a solar cover heats a pool
Transmission during the day, evaporation suppression at night. The two mechanisms separated, with the energy arithmetic for each.
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.
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.
8, 12 or 16 mil: which solar cover thickness
Thickness buys years, not degrees. The published lifespan tiers, the cost per year of service, and the case for 12 mil on a large pool.
Does a solar cover pay for itself?
The full payback derivation from one measurement you can take tonight, plus a sensitivity table for people whose pool is nothing like the example.
Clear vs blue solar covers
Clear transmits into the water, blue absorbs at the surface. Same energy budget either way — and the only published test measured no difference between them.