Heating Your Inground Pool with Solar

Solar pool heating systems can significantly reduce swimming pool heating costs. The cost is competitive with both electric and gas pool heaters, and they have very low yearly  operating costs. Actually, solar pool heating is the most cost-effective use of solar energy in many climates.


The typical solar pool heating system includes the following:

  • Solar collector — the collector transfers the heat from the sun to the pool water as it is being circulated
  • Filter — removes any foreign debris before water is circulated through the collector
  • Pump — circulates the pool water through the filter and collector and back to the pool
  • Flow control valve — there are two types, automatic or manual, which divert pool water through the solar collector.

The pool water passes through the filter followed by th the solar collector(s) by the pump. As the water passes through the collectors it is heated by the sun and then returned to the pool. During the peak of summer, the system can be used to cool the pool by circulating the water at night.

Some systems are automated through the use of sensors and an automatic valve which diverts water through the solar collector when its temperature is greater than that of the pool. If the collector temperature is the same or less than the pool temperature, pool water simply bypasses the collector(s).

Solar collectors come in several materials. Material selections dependent on your climate and the intended use of the system. In southern California, unglazed collector systems are typically used. In most cases, glazed collectors are only needed for when pools are going to be used when temperatures are below freezing. Glazed collectors use a glass covering (glaze). The unglazed collectors are made of industrial grade plastic or rubber that is treated with a UV inhibitor, thus extending the life of the panels. Unglazed collectors are built with inexpensive parts and made with a simple design, as a result, unglazed collectors are typically less expensive than glazed collectors. Most unglazed systems work best  for indoor pools in colder climates so long as the system has drain back designed drain into the pool when the pump is turned off.

How a solar collector works.

Glazed collector systems are typically built using copper tubing over an aluminum plate covered with an iron-tempered glass, which makes this system much more expensive. While, glazed collector systems are more efficient at capturing solar heat than unglazed systems making them a better choice in cold climates.

As a result, glazed collectors can be used year-round in most climates. In addition to heating your pool, glazed collectors also can also be used to heat household hot water year-round.

With either system freeze protection should be used during colder weather.


The typical solar pool heating system costs are in the neighborhood of $3,000 and $5,000 installed. Keeping in mind that the typical return on the investment is between 1.5 and 7 years, depending on your fuel costs and use in cold weather. Solar systems typically last longer than electric and gas pool heaters. Your actual cost and return on investment will depend on many factors. Therefore, talk with a pool solar expert before you purchase and install a solar pool heating system. You will need to do the following:

  • Evaluate your site’s solar resource
  • Determine the correct system size
  • Calculate the correct orientation and tilt for the collector
  • Determine the system’s efficiency
  • Compare system costs
  • Investigate local codes, covenants, and regulations.


Before you install a solar pool heating system, you will first need to access your site’s solar resource. The efficiency and design of a solar pool heating system are dependent on how much solar energy reaches your collectors.

Solar pool heating systems will use both direct and diffuse solar radiation. Fortunately, even if you don’t live in the warmest and sunny a climate most of the year, not an issue in southern California, your location may still have an adequate solar resource. In most cases, if your building location has an unshaded area and faces in a southern direction, it will be a good candidate for a solar pool heating system.

It would be best to contact a local solar pool heating system installer to assist in evaluating a proper location.


Several factors need to be evaluated when sizing a solar swimming pool heating system. Here are the most important factors:

  • Pool size
  • Length of the swimming season
  • Average regional temperatures
  • Desired pool temperature
  • Site’s solar resource
  • Orientation and tilt of the collectors
  • Collector efficiency
  • Use of a pool cover

Solar system contractors will use calculators to correctly determine the exact system requirements and collector sizing.

As a general rule, the surface area of your solar collector will be roughly equal to 50%–100% of the surface area of your pool. In cooler and overcast areas, the area may need to be increased beyond the typical ratio. The more collector square footage used will usually lengthen the swimming season.

An example, a 15-by-30-foot outdoor swimming pool in southern California will require a collector that equals roughly 100% of the pool’s square footage for year-round use. Or about, 450 square feet of collectors. On the other hand, in northern California, people typically use their outdoor pools 6–8 months out of the year, so the typical size their systems will be about 60%–70% of the pool surface area.

In any climate, you can typically decrease the required collector area by using a solar pool cover.

You will also need an adequately sized pool pump to accommodate the added pool solar system. If you’re replacing a conventional electric and gas pool heating systems with a pool solar system, you will likely need a larger pump than the one in your current system.


Collectors can be mounted anywhere that is close to the swimming pool, so long as they provide adequate exposure, orientation, and proper angle towards the sun. Typically, rooftops provide the best locations. The tilt and orientation of the collector will affect how pools solar heating system will perform. The contractor performing the installation should consider these factors when evaluating the solar resources of your site and calculating the size of your system.


The orientation of the collectors

The pools solar heater collectors should be oriented to face the path of the sun, thus, maximizing the amount of solar energy they will receive. As a general rule, the optimum orientation in the northern hemisphere will be true south, although this may be true, a recent study has indicated that, depending on the location and the tilt of the collector. A change of up to 45 often the east or the west of true south will not significantly impact performance. There are several other factors to consider, such as, roof orientation (if your mounting location is the roof), the landscape that creates shade (like trees or tall buildings) over the collector either daily or seasonally, and finally, weather conditions (foggy, marine later or cloudy afternoons). All these factors will contribute to the effectiveness of your collector’s performance capabilities.

Collector Tilt

The correct angle at which to position the collector will vary based on your distance from the equator and the length of your typical swimming season (summer only or year-round). For best performance, collectors for summer-only installation will be tilted at an angle using this formula: your locations latitude minus 10º–15º. On the other hand, a year-round heating installation will be tilted at an angle equal to your location’s latitude. However, some studies have proven that not setting collectors at the optimum angle made any significant decrease in performance. As a result, mounting collectors flat on your roof will keep the installation aesthetically pleasing and have little to no effect on performance. As a result, you will need to take the roof angle into consideration when calculating your system’s size.


The efficiency of a solar pool heating system can be determined by the collector’s thermal performance rating, when available.

A solar collector’s performance rating is measured by British thermal unit’s or BTU’s per square foot per day: Btu/(ft2day)

Sometimes, the rating will is measured unites called megajoules or MJ per square meter per day: MJ/(M2day)

It can also be measured by Btu per day, which is simply the rating in Btu/(ft2day) multiplied by the area in ft2. Also used is MJ per day, which is the rating in MJ/(M2day) multiplied by the area in M2.

Ultimately, the higher the number, the greater the efficiency of solar collection. Consequently, weather conditions, accuracies of testing instrumentation, and other testing variables, there can be inconsistencies in thermal performance between any two collectors. In the end, collectors should be considered the same as long as their ratings are within 25 Btu/(ft2day) of each other.

High-efficiency solar collectors will not only reduce your annual operating costs, but they may say reduce the footprint of the collector area needed to heat the pool.


Before you purchase a pool solar heating system, it would be wise to estimate and compare the cost savings between different solar collector models. This will help you evaluate the potential cost savings against the upfront cost of a more efficient style of the collector. In some cases, you may require fewer panels with the more efficient model saving money on installation an reducing the collector area needed to heat your pool.

To estimate and compare costs, you need to know the following:

  • The collector’s performance rating(Btu/day)
  • The total number of total collectors needed to heat your pool
  • Total of the system installed cost.
  • Thus, you can now calculate the collector’s energy output per dollar spent or invested using the following formula:

(Btu/day X # of collector panels/piping modules) ÷ total installed cost of system = Btu/$ per dollar spent


(27,900 X 4) Btu ÷ $3,000 = 37.20 Btu/day per dollar spent

If you just know the prices and performance rating of the collectors, measured in BTU’s, you may use the formula below to help you calculate the energy output for each dollar spent or invested for different collectors:

Btu/day ÷ collector price = Btu/day per dollar spent


21,000 Btu ÷ $387 = 54.26 Btu/day per dollar spent

Don’t select a solar heating system or collector solely on the estimated costs. It’s also critical to evaluate all the factors involved, including the system’s size and design quality as well as the quality of the installation.


It is important to consider local building codes and any other regulations that may govern your solar water heating installation.


The proper installation of your solar pool heating system is dependent on several factors, such as, solar resource, local weather, local building codes, and safety issues. Therefore, it is always best to have a qualified pool solar systems expert install your system.

After installation, proper maintenance will keep your system running smoothly for the next 10–20 years. Read your owner’s manual for maintenance requirements and contact your contractor if you have any questions. As long as the pool’s chemical balance and filtering system are working correctly, your collector will require little maintenance. Glazed collectors may need to be cleaned here in southern California because of limited rainfall and dusty conditions.

When speaking with potential installation/maintenance contractors, ask the following questions:

  • Are you and your company experienced at installing and maintaining solar pool heating systems?

Only choose a company that is experienced at installing and servicing the type of system you plan to install.

  • How many years of experience does your company have with solar pool heating installation and maintenance?

The more, the better. Request a list of referrals that you can contact. 

  • Is your company licensed or certified?

Having a valid plumber’s and/or solar contractor’s license is required in some states. Contact your city and county for more information. Confirm licensing with your state’s contractor licensing board. The licensing board can also tell you about any complaints against state-licensed contractors.


If you have a spa you will still need a gas or electric heating system to heat the spa on demand. But, the addition of a solar heating system will allow you to heat the pool to a comfortable temperature for extended swimming season at almost zero operational cost

Scroll Up