Solar Pool Cover Savings: Heat, Water and Chemicals

Yes, solar covers work. Evaporation is the largest way an outdoor pool loses heat, and a cover blocks it. How much money that is for you depends on how fast your pool evaporates, how much you pay for water and heat, and how often the cover is actually on.

About these numbers. The evaporation rate (1.5 in a week), the 30% share the cover prevents, the 20-week season, and the prices are example values. Measure your own evaporation with a bucket test and use your own rates. The 30% sits at the low end of the U.S. Department of Energy's (DOE) range for water savings, so the example is cautious.

Calculator: water and heat a cover keeps in the pool

Enter your pool's water surface (or length and width, or diameter), how many inches it loses to evaporation in a week without a cover, the share of that loss the cover prevents, the weeks in your season, and your water price. With the example values:

The cover keeps 144 gallons a week in a 512 sq ft pool.
Over 20 weeks, that is 2,873 gallons, worth $23 at $8 per 1,000 gallons.

Water kept = surface (sq ft) × 0.623 gallons per inch per sq ft × inches a week × share prevented × weeks.

If you heat the pool, pick gas or heat pump and enter your gas heater's efficiency or your heat pump's COP (coefficient of performance) and your energy price. The calculator then adds the heat the saved water would have carried away. The DOE says each pound of 80 °F water that evaporates takes 1,048 BTU of heat out of the pool, so heat is usually the larger part of the saving for a heated pool.

Chemical savings are not counted in the dollar total, because they depend too much on your pool. The DOE estimates that covers cut chemical use by 35% to 60%.

What the DOE says covers save

From the DOE's Energy Saver page on swimming pool covers:

Heating: covering a pool when it is not in use is the single most effective way to cut pool heating costs. Savings of 50% to 70% are possible.
Water: covers reduce the make-up water (water you add to replace losses) a pool needs by 30% to 50%.
Chemicals: covers reduce a pool's chemical use by 35% to 60%.
Cleaning: covers keep dirt and debris out, so cleaning takes less time.

The same page explains why: evaporation is by far the largest source of energy loss in pools. Higher water temperature, stronger wind, and lower humidity all raise the evaporation rate. For heated-pool cost estimates by city with and without a cover, see the pool heater cost calculator.

Measure your own evaporation first

The input that changes the answer most is your evaporation rate, and it differs a lot by climate. Measure it: set a bucket of pool water on a step, mark both levels, and compare after a few days. The bucket's drop is your evaporation. The pool bucket test walks through it and also shows whether part of your water loss is a leak, which a cover can't fix.

Convert the bucket's drop to inches per week before you enter it: inches per day × 7.

Bubble, solid, or liquid cover

Bubble (solar) covers are among the lowest-cost covers made for pools. The DOE says a transparent bubble cover may cut the sun's heating of the pool by 5% to 15%, while it blocks evaporation.
Opaque or solid covers block more light. The DOE puts their cut in solar heating at 20% to 40%. Vinyl covers last longer than bubble covers, and insulated vinyl covers add a layer of insulation.
Liquid covers are thin surface films you pour into the pool. Their makers claim evaporation savings, but we could not find an independent test, and the DOE page does not cover them. We give no percentage for them.

Whatever the type, the DOE notes that a cover saves nothing if it stays off, so how easy it is to put on and take off matters. Reels and automatic covers help.

When a cover saves less

Warm, humid weather. The DOE says evaporation drops in warm, humid conditions, so leaving the cover off during the day may be better there.
Dry or windy weather. Evaporation rises, so a transparent or bubble cover during daylight hours generally helps.
Night-only swimming. The DOE says the benefit then depends on whether the evaporation the cover prevents outweighs the sun's heat it blocks during the day.
Unheated pools where water is cheap. The water alone may be worth little, as in the example. The chemical, cleaning, and warmer-water benefits still count.

To see the cover next to your other pool costs, use the pool ownership cost calculator. If you are choosing a heater too, compare them with the heat pump vs gas heater calculator. In hot weather, also see pool care in hot weather.

FAQ

Do solar pool covers work?

Yes. A cover blocks evaporation, the largest way a pool loses heat. The DOE says covers can save 50% to 70% of heating costs and cut make-up water by 30% to 50%, if they are on whenever the pool is not in use.

How much does a solar cover save?

It depends on your evaporation, prices, and heating. In the example, a 512 sq ft unheated pool keeps 2,873 gallons a season, worth $23 in water. A heated pool saves more, because each pound of evaporated 80 °F water takes 1,048 BTU of heat with it.

Does a pool cover reduce chemical use?

Yes. The DOE estimates covers cut a pool's chemical use by 35% to 60%. A cover also keeps debris out, so there is less to clean.

Should I leave the solar cover on during the day?

In dry or windy weather, generally yes, says the DOE, since a bubble cover blocks evaporation while still letting most sunlight through. In warm, humid weather, leaving it off during the day may be better.

Sources

U.S. DOE Energy Saver, Swimming pool covers (1,048 BTU per lb; 50–70% heating, 30–50% water, 35–60% chemicals; solar gain cut 5–15% and 20–40%; when to cover; archived copy, May 2026): energy.gov via web.archive.org
U.S. EIA, British thermal units (therm and kWh conversions): eia.gov
USGS, Water density (8.34 lb per gallon): usgs.gov