When buying a solar pool heater, you may be surprised to find a range of suggestions for how many panels are needed to heat a swimming pool, but there are some guidelines that you can rely upon. The correct answer depends on your location, the orientation of the panels, shading impacts, the panel type, the panel performance rating, your desired performance, and more. However, no single factor is more important than the size of your swimming pool. When I say size, I am not referring to gallons, which many clients often provide as a starting point. The size we need is the surface area in square feet.

An ideally sized solar pool heater provides 100% coverage for the pool area.

As a rule of thumb, we recommend 100% coverage, meaning you need one square foot of solar panels for each square foot of pool surface. From there we make adjustments depending on the other factors. If you have shading issues, less-than-ideal orientation, live along an open body of water (windy), or use a separated tube panel (which performs worse in winter), you will probably need more panels. If you have a perfect south or southwest roof with other ideal factors, you may be able to get away with fewer panels. You may need to use multiple orientations to fit the number of required panels. In selecting the right number of solar panels, there is as much art as there is science. A qualified solar contractor can lead you to the right decision.

Don’t worry if you don’t have enough space or if your budget does not allow a perfectly sized system. Undersized systems and systems with sub-optimal orientation will still heat your pool every day, but they may not perform quite as well as a perfectly situated system. When you get the “ideal” 100% coverage scenario, expect your pool to reach about 10 degrees Fahrenheit above an unheated pool on most days, and 15 degrees if your cover it, especially at night. Depending on the time of year and factors that make a system sub-optimal, these systems will often provide heating that is perfectly acceptable, and will still be warmer than an unheated pool.

Since an unheated pool’s temperature varies throughout the year, so will a solar heated pool’s temperature. While there is no temperature guarantee with solar pool heating, the good news is that the resulting temperatures are comfortable for swimming 10-12 months of the year for most people in Florida without any auxiliary heating when an ideally sized system is installed.

In selecting the right number of solar panels, there is as much art as there is science.

You might be asking whether installing more panels will result in more heating performance. Why not go over 100% coverage? If you install 200% coverage, will you get a 20 degree rise in temperature? The answer is no. There is a point of diminishing returns, because as the pool water approaches the panel temperature, the heating performance (efficiency) decreases. Solar thermal systems like solar pool heaters rely on a large difference in temperature (known as Delta T) to transfer heat to the pool water. For this reason, we do not recommend installing very much more than 100% coverage, although more panels will increase pool temperature faster in the morning. If you like to swim earlier in the day and demand maximum temperature, then exceeding 100% coverage may be suitable for you.

A system with an automated controller can maximize heating performance and avoid solar panels actually cooling your pool inadvertently in inclement weather. We recommend a controller be installed with every system to increase performance and customer satisfaction. A closely managed manual system can perform almost as well as an automated system, but most owners are not diligent enough to turn their solar valve when needed, and the convenience of an automated system cannot be overlooked.

We find that most pools in Florida are somewhere in the 12’x24′ to 15’x30′ range in Florida, suggesting system sizes of 288 to 450 square feet. Using 4’x12′ panels, most solar pool heating systems require between six and ten panels with seven to eight panel systems by far the most popular.

Note that these recommendations are specific to Florida, and will vary slightly between different locations within the state.