Solar Heating for Pools and Spas

For fun in the sun

Solar pool heaters represent the majority of solar water heating systems installed in the United States. In fact, in many climates, they are the most cost-effective type of solar energy system. Their initial cost is competitive with gas and heat pump pool heaters, they last longer, and they cost much less to operate year after year.

Solar Pool Heating

Solar pool and spa heaters are simple technologies that require little maintenance. A typical system costs $3,000 to $4,000, and will pay for itself within two to seven years. What’s more, these heaters reduce greenhouse gas emissions, air pollution, and demand for fossil fuels.

Whether you heat your pool with a solar or conventional heater, a pool cover can help reduce heat loss and evaporation. Insulated pool covers are good at keeping heat in but they do prevent some of the sun’s heat from warming the pool on sunny days. An alternative is a “solar” or “bubble” pool cover. These products, which typically look like bubble-wrap packaging, are less expensive than insulated covers. Compared to an insulated cover, they let in more of the sun’s heat during the day to warm the pool, but because they’re thin and transparent, they don’t do as good a job of retaining heat when the sun isn’t shining.

This article focuses on solar heating systems for pools and spas. For heating water used inside your home, check out the “Solar Hot Water for Your Home” ¬†article or our “Fuel Cell article“.

How They Work

Solar pool heaters have three basic components: a pump, a filter, and a collector. The pump (often the existing pool pump) moves pool water through a filter to strain out leaves and other debris. Then it pumps the water into the solar collector, a series of flat panels mounted on a sunny area of the roof or ground. As the water moves through the collector, it heats up and is pumped back to the pool. Unlike solar water heaters for your home, there’s no need for a storage tank since the pool provides storage.

If you live in a region with very hot summers, you can also use the collector to keep the pool cooler by circulating the water through the collector at night, when air temperatures are lower.
If you are using a solar heater with a hot tub, you may also need a conventional backup heater to raise the temperature higher or heat it at night. A cover over the hot tub will reduce temperature loss when you’re not using it and minimize the need for backup heat.

Solar pool heaters last for 10 to 20 years. Although taking care of them is no big deal, they do require periodic inspection and routine maintenance; check with your contractor and owner’s manual for details.

Collector Types

You’ll need to choose between unglazed, uninsulated collectors and glazed, insulated collectors. The unglazed ones, which are made of a tough rubber or plastic material and don’t have a protective glass covering, are popular because they’re less expensive. But they can’t be used in the winter in climates where temperatures dip to freezing. If you live in a cold climate and have an unglazed collector, you’ll need to drain it in the winter to prevent freezing. Unglazed collectors can only be used for pools and spas, because they don’t require water that is as hot as is needed for household use. Glazed collectors for pools and spas are the same as the collectors used for heating household water. (See the article “Solar Hot Water for Your Home.”)

Size and Location

The collector is typically mounted on an unshaded portion of the home’s roof. It can also be installed on an unshaded area of the ground. Collectors perform best when facing south and tilted for maximum exposure to the sun. A solar contractor can evaluate your site and determine the best location, solar orientation and tilt for the collector.

The collector’s size depends on a number of factors, including the pool size, climate, the length of the swimming season, your water temperature preferences, how much sun the site gets, and how efficient the collector is. As a rule, the collector size needs to be 50% to 100% of the pool’s surface area. (The larger the collector, the longer you’ll be able to extend the swimming season.) If you use a pool cover, you’ll be able to get away with a smaller collector area.

Hiring a Solar Pro

Before hiring a contractor, ask the following questions:

  • Does the solar professional have experience designing and installing the type of system you want?If you are in the market for a solar pool heater, don’t hire a contractor who has only installed photovoltaic systems.
  • How many years has the contractor has been in the solar business and how many installations have they done? Solar is booming in many parts of the country; be cautious about hiring a newbie contractor.
  • Is the contractor licensed? Some states require that contractors to have special licenses; check with the contractors’ license board in your state about requirements.
  • What specific services will the solar contractor provide? Most offer a “turnkey” service: they’ll analyze your site and water heating needs, design an appropriate system, procure the equipment and materials, obtain any necessary permits, and install the system.
  • Are the bids you received based on comparable information? When evaluating bids, make sure they are for the same type and size system. The bids should include all costs associated with buying and installing the system, including hardware, installation and permits. The bids should include an estimate of how much energy will be saved compared to a gas or heat-pump pool heater.

For general advice on what questions to ask contractors and other tradespeople, see our “What to Ask Your Contractor” article.

Related Articles
Solar Pool Heating
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Passive Solar Heating
Solar Savings Calculator
Solar Hot Water Makes for Energy-Efficient Home
Why Go Solar?







  1. William October 21, 2009
  2. Joanna Cook May 14, 2010
  3. rstepanov May 14, 2010

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