How To Optimize Your Solar Pool Heater


How To Optimize Your Solar Pool Heater

To optimize the use of a solar pool heater, it’s important to understand the heat losses and gains from swimming pools. Heat losses from a pool occur primarily through evaporation from the surface, convection and infrared radiation.  This post will explore how to optimize your solar pool heater by mitigating some of the heat losses that are common from swimming pools.

Evaporation can account for as much as 70% of heat losses in a pool.  The endothermic process of evaporation of water, cools the remaining water in the pool.  Each gallon of water that evaporates removes approximately 8,300 Btus of heat from the pool.   On the contrary, warming a gallon of replacement water to the temperature of the pool, requires only 8.3 Btus per degree Fahrenheit of temperature increase or between 80 and 200 Btus per gallon for the typical heat gain required. The relative humidity of the ambient air regulates the evaporation losses, where a lower relative humidity in the ambient air leads to higher evaporation losses, and humid ambient air results in lower evaporation. The wind speed affects the convection loss to a high extent. Convection can be defined as the movement caused within a liquid by the inclination of hotter and therefore less dense material to rise, and colder, denser material to sink under the influence of gravity, which subsequently results in transfer of heat.


Losses from conduction to the ground are typically small and are often ignored in warmer climates. Outdoor pools can lose some heat via infrared irradiation exchange with the sky.  A transparent cover is an effective way to reduce heat loss from evaporation when a pool is not being used. Air pockets in the cover will reduce convection losses. Savings from pool covers depend on how long the pool is covered and on the local conditions which may impact evaporation.   Additional savings are achieved because less makeup water is required including additional chemicals to ensure the proper pool chemistry. It’s important to note however that water on top of cover (e.g. after rain or leakage) will have a cooling effect. This is due to the fact that as the water evaporates and cools the pool water below, if there is no insulating gap.

Heat gains to a pool may come from direct solar radiation or convection when the ambient temperature is higher than the pool temperature. Transparent covers allow direct solar radiation in the pool while reducing the evaporative losses. Short wave radiation enters the water depending on the wavelength of the radiation. Well-functioning pool covers act as selective transmitters. The covers admit the shorter wavelength radiation of the solar radiation and are reflective of the long wavelengths of the infrared radiation. The infrared radiation accounts for the radiation heat loss e.g. to the cold sky or surroundings. Pool covers reduce the heat loss by evaporation during the day and the radiant heat loss during the night. Researchers have confirmed that the heat losses are dominated by evaporation from the surface of the pool and a cover over the pool at night time significantly reduces the heat losses.


In conclusion, pool covers block evaporation as well as radiant losses and can provide some insulation from convective losses.   Solar collectors with an area of 50% of the pool surface can work well for heating the pool.  A case study showed that unglazed solar collectors with an area of 62% of the pool surface kept the pool at the required temperature level of 80-85 °C during the colder months.  Implementing these strategies for increasing the pool temperature resulted in an almost doubling the days of the swimming season.  Also, sheltering off wind can significantly reduce heat losses.

Another Reason to Utilize Solar Pool Heaters – Safety

solar pool heater benefits

Another Reason to Utilize Solar Pool Heaters – Safety

The many benefits of using a solar pool heater include using renewable energy, reducing your carbon footprint and air pollution, saving money on utility bills.  Another important reason to switch from a gas pool heater to a solar pool heater  or solar pool heating system is safety.  Natural gas and propane are combustible and can leak resulting in a build up of highly flammable gases.   Incomplete combustion also results in the release of carbon monoxide, an odorless and invisible deadly gas. Two accidents illustrate these safety concerns.

One recent incident occurred on May 6, 2015 when a man was injured by an explosion from a propane pool heater.  Authorities report that a propane delivery employee from Mechanicville was injured in an explosion in Clifton Park while delivering propane for the homeowners’ pool heater.  After the tank was filled, officials say he went inside the pool shed to light the heater, at which point there was an explosion.  The employee was transported by helicopter to the Westchester Burn Unit for treatment. The victim suffered burns to 52 percent of his body. According to investigators, the cause of the explosion is still under investigation. The shed was the only building damaged by the explosion, and no one else was injured. When using gas pool heaters it is highly recommended that people periodically check piping and hoses to make sure there are no leaks. It’s not unusual for animals to chew through hoses after being attracted by the smell of propane.

solar pool heater benefits safetysolar pool heater benefits safety 2

When a gas pool heater is not installed properly a number of problems can occur including the build up of carbon monoxide gas. A qualified and very experienced professional should be used to install the gas pool heater safely. There are several components to a heater to install to include: Gas, electric, and plumbing. Proper ventilation and correct placement are very important when installing gas pool heaters. Exhaust from gas pool heaters contains toxic levels of carbon monoxide, a dangerous and poisonous gas. According to a 2004 report from, “Carbon monoxide poisoning may be more common than is currently recognized. It is conservatively estimated that in the US there are at least 200 deaths per year from carbon monoxide poisoning.” An unfortunate example as to the importance of proper installation procedures is the case of former tennis star Vitas Gerulaitis. The retired tennis super stars’ life was tragically cut short due to carbon monoxide poisoning as he napped in the room directly above the pool equipment at a friends’ house. Insufficient ventilation led to a deadly amount of carbon monoxide that resulted in his tragic death. With a $1.44 pipe extension, the fumes would have been dispersed safely away from the cottage. Instead, the carbon monoxide was drawn by an air conditioner through a forced-air heating vent into the cottage where Mr. Gerulaitis was sleeping. When he died, the carbon monoxide level could have reached 2,700 parts per million. The Immediately Dangerous to Life and Health (IDLH) limit for carbon monoxide is 1200 parts per million and the OSHA 8 hour limit is 50 parts per million. Carbon monoxide is an odorless and invisible gas with symptoms of poisoning that include dizziness, headache, nausea, weakness, sleepiness, muscular twitching, vomiting and inability to “think clearly”. Excessive exposure can result in brain damage or death.  If you experience any of the symptoms, immediately turn off the pool heater and leave the vicinity….and get into fresh air immediately. The pool heater must be thoroughly tested by a gas professional before resuming operation.

Solar pool heaters utilize energy from the sun and do not result in any exhaust such as carbon monoxide or combustible levels of highly flammable gases. Solar pool heaters are a wise investment for many reasons including financial (quick return on investment), environmental and financial.

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Commercial Solar Pool Heating Case Study – Perth College

Perth College, located in Mt Lawley, is the oldest independent girls’ school in Western Australia.  It has a large outdoor pool which is heated by a gas heater. The 50 meter eight-lane swimming pool is utilized by the school as well as the Perth City Swimming Club and by the Perth Swim Academy, to promote education, instruction and development of swimming sports.

Motivated by the desire to lower its gas bills to heat the water and reduce CO2 emissions, the school decided to install an evacuated tube (EVT) solar pool heating system.  This is an excellent example of the utilization of a commercial solar pool heating system.  Such a system can produce twice the heat per unit area as a traditional flat plate panel system, and because of its high efficiency it can maintain warm pool temperatures in the colder months.

commercial solar pool heating

The solar pool heating system was installed by Supreme Heating WA and includes a 72-panel EVT system. Supreme Heating WA was able to complete the project in approximately five weeks. The system is designed to generate very high water temperatures needed copper fittings to handle the temperatures.  The Viega Propress system was utilized and Viega assured them that their fittings would sustain temperatures up to 200°C.

Evacuated tube (EVT) collectors were developed more recently than flat plate collectors. Introduced to the market in the 1970’s, there are several varieties of evacuated tubes.   The most commonly used type utilizes a heat pipe surrounded by a glass tube under a vacuum.

  1. The glass tube consists of two walls of glass.
  2. In between the two walls, all the air is removed, resulting in a vacuum.
  3. The vacuum is ideal for insulation and has much better heat retention than air space.
  4. The heat pipe is also pressurized, allowing the liquid (usually water) to boil very rapidly, at a very low temperature (usually between 75F and 80F).
  5. As the water boils, it carries the collected heat to the top of the collector, where the heat is then absorbed by water or heat transfer liquid that flows.

evacuated tubes - solar thermal

Cost is typically the primary consideration. Collector for collector, evacuated tubes can cost around 20% to 40% more to buy than flat panel collectors. However when comparing price one should consider cost per BTU capacity, and consider year round performance. In cool climates, evacuated tube collectors will have a lower cost per BTU.


Solar Pool Heater Installed at the Fort Belvoir Army Base in Fairfax County Virginia


In an effort to reduce their carbon footprint, the Fort Belvoir Army base in Fairfax County Virginia, recently installed a solar pool heating system for its Benyaurd Indoor Pool.   The solar system was completed and connected on March 19, 2014.  The solar pool heater is expected to save over $11,000 per year in energy use.   This represents more than 40 percent of the annual cost to heat the indoor pool using natural gas.

Solar pool heater

 Renewable Energy Focus

The Energy Policy Act of 2005 (EPAct 2005) established a number of energy management goals for Federal facilities and fleets.  Executive Order (E.O.) 13423, Strengthening Federal Environmental, Energy, and Transportation Management, was signed on January 24, 2007, to strengthen key goals for the Federal Government.  It set more challenging goals than the Energy Policy Act of 2005 (EPAct 2005) and superseded E.O. 13123 and E.O. 13149.  E.O. 13423 requires Federal agencies to reduce energy intensity by 3% each year, leading to 30% by the end of fiscal year (FY) 2015 compared to an FY 2003 baseline. This goal was given the weight of law when ratified by EISA 2007.  Accordingly, the Fort Belvoir Army base set its energy reduction goal at 30 percent by fiscal year 2015.


The Solar Pool Heating System

The solar pool heater works in combination with the existing natural gas fired heater.  The gas heater will be utilized on days when the sun’s radiant energy is suboptimal. The system sends filtered pool water to the solar collectors when usable solar energy is available. Pool water is heated as it flows through the collectors before being returned to the pool.  When the preferred temperature is reached, the solar system is bypassed, and pool water completes its normal circulation loop.

There are 80 4’ x 12’ Aquatherm Solar Industries solar collectors heating the pool with a total of 3,000 square feet of collector area.   A SPEC Model-95 pump was installed downstream from the filter functioning as an inline booster pump.  When the solar is on, the 5-horsepower pump sends 260 gallons per minute through the collectors.

Instead of screwing attachments to the roof membrane, the collector array was mounted to on a long-lasting composite wood-alternative, which was secured to the membrane roof with an adhesive and sealant, as well as additional pieces of the same membrane material.

Solar pool heating for the Benyaurd Pool is the most cost-effective form of pool heating, with no additional operating cost, low maintenance and a limitless supply of heat from the sun.  When the sun’s intensity permits and ambient outside temperature is above 40- to 50-degrees Fahrenheit, the solar system is the primary source of heating the pool.   The system will raise the unheated water temperature by 10 to 15 degrees Fahrenheit until the pool’s desired water temperature is reached.

Benyaurd Pool 2

The solar system used to heat the pool was manufactured by Aquatherm Industries, Inc. of Lakewood, New Jersey, and is specifically designed for low-temperature applications. The unglazed solar thermal collectors can efficiently heat water to a maximum temperature of up to 100°F – perfect for heating a swimming pool.  The polymer solar collectors are constructed of durable, UV-resistant polypropylene and have an average life expectancy of 15 years according to Aquatherm.

Benefits of Solar Pool Heaters

solar pool heater Benefits

Here are several benefits of utilizing a solar pool heater to warm your pool:

  1. More economical over the life of the system than a pool heater that uses electricity, fuel oil or propane gas.  Compared to other pool heating technologies, a solar pool heating system pays for itself within 2 to 4 years.
  2. Uses clean energy / reduces your carbon footprint–  Solar energy is a versatile, clean and inexhaustible fuel source.  Solar radiation (heat, light and other radiation emitted from the sun) is the primary energy source for almost all natural processes on earth. The sun provides massive amounts of renewable energy that can be harnessed to provide us with heat and electricity.  Each hour the sun gleams onto the earth more than enough energy to power the world for an entire year.
  3. It is relatively simple to integrate a solar water heater since most pools require a pump, filter, and plumbing.
  4. Provides the lowest maintenance costs (minimal if any).
  5. Has the longest lifespan (no moving parts, no corrosion) – almost always outlasting their warranties.
  6. Adds value to your home.

Selecting a Solar Pool Heater

A number of factors will affect your decision on selecting the best solar pool heater for your particular needs.  The cost of the system is one significant factor.  The cost of a solar pool heating system ranges from $3,000 to $7,000 to buy and install.  The return on investment  is between 1.5 and 7 years, depending on your local fuel costs.  Solar pool heaters typically last longer than gas and heat pump pool heaters. The actual cost and payback are contingent on several factors.  Prior to purchasing and installing a solar pool heating system, you should complete the following:

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