Solar cover on or off during the day?
On, unless you are swimming or the pool is already where you want it. The reason is that evaporation does not stop at sunrise.
Quick picks
The reel first, deliberately: this page's advice only works if deploying the cover is trivial.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 | No photo What makes this practical Blue Wave Solar Cover Reel On, off, on again is only realistic if it takes thirty seconds. | Any inground pool with a cover you are not using enough | |
| 2 | No photo The cover to do it with Sun2Solar 1200 Series Crystal Clear Solar Cover Clear transmits during the day and seals at night. Light enough to handle daily. | Most pools, most budgets — the default recommendation |
#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 short answer
Leave it on, unless somebody is swimming or the pool is already at or above the temperature you want.
The instinct to take it off during the day comes from thinking of a cover as a lid that blocks the sun. It does not work like that — a solar cover is designed to transmit or absorb solar energy into the water, and it does that job with the cover on.
Why on is usually right
Because evaporation does not stop when the sun comes up. It accelerates. Warm water, warm air and afternoon breezes are the conditions evaporation likes best, and DOE’s figure for a mere 7 mph wind across the surface is a 300% increase in energy consumption.
Seven miles an hour is a light breeze — leaves moving, a flag stirring. On an open site, a breezy afternoon with the cover off can lose more heat than the sun is putting in.
| Solar gain, clear midday sky | about 105,987 BTU/hr into a 16 x 32 pool |
| Evaporative loss, still air | the baseline |
| Evaporative loss at 7 mph wind | 4x the still-air rate, per DOE |
We are not going to put a single number on afternoon evaporative loss, because it depends on humidity and water temperature and we have no fetchable source that quantifies it for a residential pool. What DOE's wind figure does establish is the direction and the scale: on a breezy day, leaving the cover off can cost more than the sun gives.
The two times to take it off
1. When somebody is swimming. Obviously — and it is worth saying plainly that a solar cover is not a safety cover. It will not support weight, and a person or animal that gets under one is in serious trouble because the material clings. Never leave a solar cover partly on an unsupervised pool.
2. When the pool is already too warm. This is a real situation on small above-ground pools in high summer, where the water can overshoot comfortable. Taking the cover off during the day lets the pool shed heat by evaporation — which is precisely the mechanism you spend the rest of the year fighting. Put it back on at dusk if you still want the overnight retention.
The case for a routine
The best pattern for most pools is boring: cover on except when the pool is in use. Not a schedule, not a rule about daylight — just on by default.
Whether that is achievable comes down entirely to how long it takes. Thirty seconds with a reel is a habit. Five minutes and a second person is a thing that stops happening in June. If your honest assessment is that you will not put it back on after swimming, rings or a liquid cover get you part of the way with none of the friction.
One thing to avoid
Do not leave a cover on a pool you are not treating. Under a cover, with circulation off and chemistry drifting, a warm pool is a good environment for algae — a clear cover especially, since it lets light through. The cover is not the cause, but it will not save you from neglected chemistry, and it makes the consequences harder to see.
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.
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.
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.
Questions people actually ask
Should I leave my solar cover on during the day?
Does a solar cover block the sun from heating the pool?
Can my pool get too hot under a solar cover?
Is it safe to leave a solar cover on the 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
- 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
- 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
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.
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.
Solar cover reels
Why a reel is the highest-leverage buy in pool heating, and which ones to look at. Thirty seconds alone versus five minutes and a helper decides whether a cover saves anything.
Solar covers for above-ground pools
Why fit matters more than thickness on an above-ground pool, and the arithmetic showing why a small pool responds several times faster to the same sunlight.
Do solar pool covers work?
The 4-degrees-versus-15-degrees contradiction that runs through this entire category, reconciled from published physics. Three different quantities being reported as one.