Solar Pool Heaters Can Lower Energy Costs

By: Julie Sturgeon
Published: March 25, 2010

A solar heating system should be installed on the south-facing side of a roof so it can absorb the most sunlight. Image: Aquatherm Industries, Inc.

Homeowners in search of a greener and more economical method of keeping their swimming pools warm are harnessing the sun’s energy. Solar pool heaters can lower energy costs because they rely primarily on a free and renewable energy source, rather than electricity or natural gas.

Solar pool heaters cost more upfront than traditional alternatives, perhaps 50% more than electric heat pumps and several times more than gas heaters. However, the payback can come in as little as two years, depending on local utility rates and other factors.

How solar pool heaters works

A typical solar pool heating system centers around large plastic solar collectors installed on the south-facing roof of a house. A pump circulates pool water through the collectors, where it’s heated gradually. A return line takes the warm water back to the pool. Professional installation of a system takes about a day.

The setup is similar to a solar-thermal water heater that’s used to heat water for use inside a home. A key difference is the collectors used for solar pool heating are less sophisticated (and cheaper) because water for a pool only needs to rise a few degrees, vs. tens of degrees for indoor use. A typical pump will send all the water in a pool through the collectors twice in 24 hours.

A solar heater typically can raise a pool’s temperature by 15 degrees Farenheit. Optimal conditions are subjective, but 80 degrees should be comfortable for most swimmers. Teenagers might be willing to dive in when the temperature is in the 70s, while some people won’t dip a toe in the water until it reaches 90 degrees.

How quickly the temperature can rise depends on location. Texans can see a 5-degree increase in a day, while in Alaska it may be less than a degree every 24 hours. Cooler air temperatures, cloudy skies, and fewer daylight hours all affect the performance of solar pool heaters, which require little maintenance and usually last 10 to 20 years.

Cost of solar pool heaters

Solar pool heaters are more popular and cost-effective in sunny states like Florida, Arizona, and California, where the systems have penetrated as much as 60% of the residential market. In the East and Midwest, where sun isn’t as plentiful and utility rates are more reasonable, it can take longer to realize the economic benefits.

A typical solar heating system might run between $4,500 and $7,000 installed, depending on pool size, according to manufacturers. Electric heat pumps, the most popular alternative, cost $3,500 to $4,500; gas pool heaters, the least efficient option, run between $1,000 and $1,500.

Breaking even on a solar pool heater will depend on several factors, especially local utility rates. Manufacturers estimate a typical homeowner will see a return on investment in two to five years vs. a gas heater. The U.S. Department of Energy puts the payback period between 1.7 and seven years.

The federal energy tax credit doesn’t apply to solar heating for pools, but some states offer incentives. For example, Arizona gives tax credits and sales-tax rebates to homeowners who install solar pool heaters.

Roofs can make or break decision

Systems must be sized by a pro. Generally, the surface area of the rooftop collectors should be equal to 85% to 100% of the surface area of your pool. In areas that don’t get substantial sunlight, that percentage might climb as high as 150%.

The size and condition of your roof help determine whether a solar pool heater is right for you. Collectors require a lot of square footage on a south-facing roof. The installer will also need to make sure the roof is sound enough to support the collectors. Older roofs may need repairs or replacement, adding to the project cost.

There’s also the issue of sun exposure. A solar pool heater doesn’t work well on cloudy days or when collectors are blocked by shade. In general, heat pumps can raise water temperatures faster and more reliably than solar heaters, albeit at a higher cost. If budget isn’t a concern, you can install a heat pump as a backup.

Solar blankets are a must

To keep heat from escaping, homeowners should use solar pool covers, sometimes called solar blankets. Covering a pool with a floating solar blanket when it’s not in use not only keeps heat from escaping, but also adds another 5 degrees to the water temperature. As well, solar blankets reduce evaporation, which lowers the amount of replacement water and chemicals needed.

The cost of solar blankets varies depending on size and quality, but figure a good-quality blanket that’s 12 feet by 24 feet will run about $100. The blanket can be spread over the pool surface (and removed) by hand, or plan to spend at least a couple of hundred dollars more on a reel system.

A solar blanket pays for itself. Even in balmy Miami, it can cost $2,848 a year to heat an uncovered 1,000-square-foot outdoor pool to 80 degrees using an 80% efficient gas heater. The cost is $1,460 when an electric heat pump is used instead. But in conjunction with a solar blanket, those annual costs plummet to $584 and $300, respectively.

Julie Sturgeon has written about residential pools for nearly a decade. She can’t take advantage of solar heating because her roof is shaded on all sides.