Solar Pool Covers: Do They Work and What Size Do You Need?

A solar pool cover works: it floats on the water, slows evaporation and helps the pool keep the heat it gains from the sun. The EPA says a cover can prevent up to 95 percent of evaporation. Size it by the pool’s inside measurement, so an 18 ft round pool takes an 18 ft round cover.

How a solar pool cover keeps a pool warm

A solar pool cover, also sold as a solar blanket, is a sheet of plastic with air bubbles on one side. It goes on the water bubble side down. Intex, a maker of above-ground pools, describes the bubbles as absorbing sun heat and passing it into the water, while the cover insulates the pool and cuts evaporation. Inyo Pools, a pool supply retailer, adds that the trapped air insulates the water against wind and cooling at night.

The EPA’s WaterSense program lists the main benefits of any pool cover:

• Much less evaporation, which means less topping up with the hose.
• Water that holds more of its heat when the cover is used consistently.
• Less cleaning and lower chemical use.

A cover fits almost any pool. WaterSense says covers work on indoor and outdoor, in-ground and above-ground pools of nearly any shape, and come in manual, semi-automatic and automatic versions. A solar blanket is the manual, low-cost end of that range.

WaterSense once planned a label for pool covers and dropped it. Its reason is useful for shoppers: all solid pool covers save water when used properly, and the savings differ little between many types. The habit of putting the cover back on matters more than the brand.

Clear, blue or black: which solar cover color to pick

Most covers come in clear or blue, and some in darker colors. Inyo Pools says a clear cover lets more of the sun’s heat reach the depths of the pool, while a blue cover tends to soak up heat itself, so the blanket warms more than the water. That is the retailer’s reasoning rather than a lab test, and every color still blocks evaporation, which WaterSense treats as the main saving.

Thickness is sold in mils, or thousandths of an inch, and warranty length varies between covers. Compare the mil rating and warranty on each listing rather than going by color alone.

What size solar pool cover do you need?

Covers are sold by pool size, and the way to measure depends on the shape. Inyo Pools’ sizing guides give these rules.

A solar cover sits on the water inside the pool wall, so buying the size printed for your pool, then trimming, gives a snug fit. To trim, lay the cover on the water with its seams running parallel to the sides of the pool, let it settle, and cut the edges with heavy-duty shears.

Solar pool cover safety

Take the cover all the way off before anyone swims, and keep children away from a covered pool. A cover reel beside the pool lets one person roll the whole blanket off at once.

Getting the most from a solar cover

Treat the cover as the pool’s lid. Inyo Pools points to wind and nighttime cooling as the losses the bubbles guard against, so the cover does the most good from evening to morning and on breezy days. Put it back on after each swim, bubble side down, and check that it lies flat across the whole surface with no gaps at the wall. For other ways solar power can help around the yard and garden, start at our pool and water section, which also covers solar water pumps for wells and stock tanks and solar bird bath fountains. For solar power more widely, see the solar panels section or our guide to grid-tied vs off-grid solar.