This section shows how lower your cost of heating an outdoor swimming pool and operating its filtration pump, and how to reduce the water lost due to evaporation. Much of this applies to outdoor hot tubs and indoor pools, but these are not dicussed.

Energy Conservation Measures

  • Build a wooden fence around your pool as a windbreak. Blocking the wind will lower your heating costs. Water looses much heat through evaporation, and wind blowing over a body of water greatly increases its evaporation rate. The Department of Energy has estimated that a 7 mph wind blowing constantly over a pool’s surface would increase the cost of heating a pool by 300%. You can roughly estimate your savings by computing 300% of your pool heating cost, and then estimating the percentage of time the wind blows over your pool. Multiply this percentage by the money you would save if the wind were reduced from blowing 100% of the time to being completely blocked. Building an attractive wooden fence may pay for itself by increasing the property value of your home.

  • If you have a wooden fence as a windbreak, remove any tall shrubbery growing near the pool, because they will not break the wind. Debris from them can clog the filter, making it inefficient and more expensive to operate.

  • When your filtration pump fails, replace it with a two-speed pump and use the lower speed, or replace it with a smaller pump. Using either of these, you must filter the water many more hours each day at a low pump speed, and you will greatly decrease the energy used by the pump, and clean the water just as well. See Appendix D, “Filtration Pumps that Use Less Energy”.
  • Keep your pool filter clean. This will allow you to operate your pump less hours per day to save energy. A very dirty filter decreases the flow of water through the pump, requiring it to run more each day. Pool filter systems have pressure gauges that measure the water pressure upstream and downstream of the filter, and you clean the filter when the pressure difference exceeds the value given by the manufacturer.
  • If your pool is heated by gas, propane or a heat pump, hire a technician to do a tune up if one hasn’t been done in years. This will improve the heater’s efficiency. It may not be cost effective to do a tune-up every year. Heat pump pool heaters need to be serviced the most often. They have refrigerant which leaks out, making them less efficient. If your pool has a heat pump pool heater, see Appendix C, “Heat Pump Swimming Pool Heaters”.

  • If you have a heated pool and a pool cover that is too much effort to put down for only short periods, buy a pool cover that is easy to put down to use for short periods. Use it whenever you are not using the pool, even for one day. Don’t replace the cover you have because it should be used in winter, especially if it is a safety cover. Pool covers that are easy to put down include solar pool covers, vinyl pool covers that you roll up with a reel, and motorized pool covers. If you have an above ground pool, you can make your cover much more convenient to use by mounting a pool cover saddle to the side of the pool. If you have one of these types, use it whenever you are not using the pool. If you cover your pool on the days you are not using it you will lower your cost of heating the pool, and the cost of water lost to evaporation. Also, your pool water will be cleaner, so you can run your filtration pump less, saving electricity. If it rains often where you live, covering your pool will reduce the problem of the rain changing the pH level of the water.

Covering the pool reduces the heat lost in two ways when the pool water is warmer than the air. On a typical day, 30% of the energy lost is due to thermal radiation, 60% is due to evaporation and 10% is due to conduction into the ground. A cover reduces the thermal radiation, and an insulated vinyl pool cover or a solar pool cover reduces it much more. Secondly, the cover blocks evaporation, and water removes much energy as it turns to vapor and evaporates. Every gallon of water that evaporates takes with it 8500 Btu’s, and pools lose about 1” to 1½” of water per week under typical weather conditions. For a 1000 sq. ft. pool, an inch of water equals 625 gallons, which will remove 5,000,000 Btu’s as it evaporates.

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                            Energy lost from hot water in heated pool on a typical day

When a pool is uncovered or has a clear cover it absorbs most of the sun’s energy that hits the surface. Thus, if the water is only a little warmer than the air and the sun is shining, there may be no advantage in covering the pool. The exception is using a clear or light blue solar pool cover, which allows solar energy to pass into the pool and is insulated to retain the heat. These are made of a material that appears like bubble wrap. Light blue solar pool covers, which are very popular, are almost as effective. A clear or light blue solar pool cover can be compared to a car windshield: on a sunny day, more heat energy enters than escapes, making the air in the car hot. Energy enters a pool (or car windshield) as solar energy, i.e., UV radiation, and escapes as heat energy, i.e., infrared radiation, which has different properties. Solar pool covers also insulate well, reducing energy loss due to thermal radiation. They are described in Appendix B, “Solar Pool Covers”. Black solar pool covers are also available, which can become hot under enough direct sunlight. Their manufacturers claim that they become hot and transfer the heat into the pool. They are not very popular, presumably because they are not more effective than clear or light blue solar pool covers.

The water and energy your pool will lose due to radiation and evaporation each vary from day to day based on the temperature, humidity, sunshine and wind. There is much more energy lost to radiation on a cold day, much more lost to evaporation on a windy day, and less evaporation on a humid day. You may check the forecast before deciding whether to cover your pool.

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                   Solar pool cover material                                                 Solar pool cover on a reel



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                                           Pool cover reel system

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                                           Pool cover for above ground pool a saddle

  • Reduce the pool filter operating time to 4 to 5 hours per day, then check that the water remains clean. It will be clean if the main drain cover is visible from the deck. You may increase this time if many people use it every day. Reducing the time to 4 to 5 hours could reduce your consumption of electricity by the pump by 40-50%.

  • Set your filter timer clock to run the filter when the cost of electricity is lowest, which is before dawn.

  • To save energy, carefully choose your pool’s water temperature. Reducing the temperature by one degree should lower the cost of heating the pool by from 10% to 30%. If you heat your pool by 5º, for example, lowering the temperature by 1º will reduce your costs by about 20%. Keep a thermo- meter in the pool to monitor the temperature. A temperature of 80º is comfortable to most pool users, so try 77º, 78º and 79º. The American Red Cross recommends a temperature of 78º for competitive swimming, but this may be too cool for young children and the elderly, who may require a temperature of 80ºF or higher.
  • Turn on the heating system and record how long it takes for the water in your pool to heat up to your favorite water temperature. Do the test twice, when the water temperature is 10º, and 20º below your favorite water temperature. Use the results to make a straight line graph, and use this to estimate how long it takes to raise the temperature by 5º, 15º, 25º, etc. Post the results as a table or a chart, near the pool. Check the water temperature and turn on the heating system just in time to heat the pool to the desired temperature.

  • If you are installing a pool heating system, buy an efficient pump, motor, and pool heater, and of the capacity that is most efficient for your pool. They must be sized by a trained professional. Gas heaters with efficiencies as high as 97% are available; propane heaters can be 90% efficient.
  • If you heat your pool often, it may be a good investment to replace your heating Swimming Pools_html_m1fcfd38esystem with a solar pool heating system. Solar heaters for in-ground pools use solar panels mounted on the roof or in the yard. For above-ground pools, several solar panels may be mounted along the side of the pool, or small, round, “beehive solar heaters” can be rested on the ground. 




                                                                                            In-ground pool with solar pool heater 

 For any solar heating system to be a good investment, your home must be “solar feasible”, which means there is room for the solar panels on the roof, basically facing south, or else they can be mounted on the ground and there is enough sunlight and other factors. If these conditions are not ideal the solar collector may need to be as large as the pool. See Appendix A, “Solar Pool Heaters”.

  • If you want to heat your pool with a solar pool heater but pay much less for it and you have home improvement skill, you can build one yourself. There are do-it-yourself magazines and web sites that give good instruction on how to build one. You order solar glass sheets or solar tubes, designed for do-it-yourselfers to use to build solar heaters. A very inexpensive, but not very effective design is to make a labyrinth of black PVC pipe, resting on a black surface, to collect the heat. Some designs include a wheeled trolley so you can move the panel away when not using the pool.

  • If you are considering buying a gas, propane or resistance electric pool heater, it may be more cost-effective to use a heat pump pool heater. These are electric, but like residential heat pumps, they cost less to operate than heaters that use other types of fuel when the weather is relatively warm. They cost much more to purchase, so they are only a good investment if you heat your pool often. See Appendix C, “Heat Pump Swimming Pool Heaters”.

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                                                     120,000 Btu pool heat pump

Appendix A Solar Pool Heaters

There are several types of solar pool heating systems. In each of them, the pool’s water is pumped through a solar collector where it is heated. The main types are:

1. Solar pool heating systems for in-ground pools. These have a very large solar collector made of solar panels. It may be mounted on the roof or on the ground.

2. “Beehive” solar heating systems. These have one or two small, round solar collectors which are mounted on the ground. They are only used for above-ground pools.

3. Solar pool heating systems with solar panels for above-ground pools.

If you install a solar pool heating system for an above-ground pool, you do not have to replace your filtration pump. The water is pumped through the filter, then through the solar collector, with your existing pump. If you install a solar pool heating system for an in-ground pool you may or may not need to replace the pump with a larger model.

There are several types of solar heaters designed for above-ground pools. With the exception of those that use solar panels, they are all too small to receive enough solar radiation to heat a pool by more than a few degrees. For most, if not all models you can use two in series. Be wary of advertisements that claim these products can “make your pool water warm”. Thus, you could not use a solar heating system to heat an above-ground pool, in place of a heater that burns fuel, except possibly a heating system with several large solar panels.

  1. Solar pool heating systems for in-ground pools

If you have an in-ground pool, the only way to heat the pool effectively with solar energy is to install a system with a large solar collector made of solar panels. Depending on where you live, the solar collector may need to be as large as the pool. The disadvantages to solar pool heating are that the heater can’t begin to heat the water before the sun comes up, and it can’t always make the water warm enough, especially on windy, cloudy or cool days. If you now have a gas or propane heater and will be installing a solar pool heater, you could keep your old heater maintained to use on these days by connecting it in series with the solar pool heater.


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In-ground pool heated by solar collector in conjunction with conventional pool heater

One would presume that solar energy has the best payback in the states with the most sunshine, but this isn’t true. The states with the shortest payback periods are those with the highest state incentives for installing solar, together with the highest electricity rates. In fact, Massachusetts has one of the best payback rates.

However, installing a solar collector on your roof may not be permissible in your jurisdiction or homeowner’s association. This is explained below.

Many solar pool heater manufacturers claim that their systems can be installed by do-it-yourselfers. A problem with doing this is that you should have a professional pool installer select a solar collector, pump, and filter of the correct size, and an installer may not do this if he is not installing it.

The manufacturers may claim that their solar collectors last 10 years or 20 years.

A solar pool heating system with a solar collector, for an in-ground pool, will include some or all of the following components:

  • Solar collector — the device through which pool water is circulated to be heated by the sun

  • Filter — removes debris before water is pumped through the collector to help it to maintain its high efficiency.

  • Strainer — removes leaves and sticks.

  • Filtration pump — circulates water through the filter and collector and back to the pool.

  • Flow control valve — automatic or manual device that diverts pool water through the solar collector

Some solar pool collectors have a glass cover, i.e., they are glazed, and some are un-glazed. GlazedSwimming Pools_html_m565ac5f3 collector systems are generally made of copper tubing on an aluminum plate with a tempered glass covering. They capture more heat than un-glazed systems in cold weather because the heat is trapped by the glass, but they may be less cost-effective in warmer weather due to their higher price.  


                                                                                                                       Solar panel

A solar pool heating system typically costs between $3,000 and $4,000 to buy and install. In all areas of the country it is a risky investment. In most states it would probably take over 10 years to recoup the investment. If you sell your home sooner than you had planned and you remove the solar collector, (at the realtor’s advice), it may have been a poor investment. If you use your pool much less than you had planned, and thus would pay to heat it less, it will probably have been a poor investment. If the system fails, the warranty may not cover it because the company may have gone bankrupt. The time it would take for you to recoup your investment will depend on your fuel costs, your climate, the system’s efficiency, and the state incentives for solar energy. Before selecting a solar pool heating system, you or your contractor should do the following:

1. Evaluate your site’s solar resource-how much direct and diffuse solar radiation would reach the collector.

2. Determine the correct system size. The contractor should include all of these factors in his calculation:

Pool size

Length of swimming season

Average temperature

Desired pool temperature

Site’s solar resource

Collector orientation and tilt

Collector efficiency

Whether a pool cover will be used.

The surface area of your solar collector should equal about 50% of the surface area of your pool in the hottest, sunniest regions, and about 100% in the coolest and cloudiest regions. In any climate, you can usually decrease the required collector area by using a pool cover many days each year. If you’re replacing a conventional pool heating system with a solar system, you may need a larger pump, or a separate, smaller pump to move the pool’s water to and through the collectors.

3. Determine the correct orientation for the collector

A collector can be mounted on the roof or on the ground near the swimming pool if there is adequate exposure to the sun, and the orientation is basically southward, and there is sufficient tilt. The optimum orientation is true south, but depending on the location and collector tilt, the collector can face up to 45º east or west of true south without greatly decreasing its performance.

4. Determine the optimum tilt for the collector

The optimum tilt depends on your latitude and the length of your swimming season. However, not having a collector tilted at the optimum angle will not significantly reduce system performance, so you can usually mount collectors flat on your roof, for better appearance at very little loss of efficiency.

5. Estimate the payback period for several models. The estimated payback period will be different for each model because they have very different efficiencies and different costs. The efficiency is given by the manufacturer as the “thermal performance rating”, but is not available for all models.

The efficiency of all solar panels decreases each year, but the decrease is small and somewhat predictable. A good estimate is that they lose about 3% of their effectiveness (and efficiency) the first year and 1% each following year. Most solar companies guarantee that their products are 90%effective after 10 years and 80% after 25years, which is another way to estimate the decrease in efficiency.

7. Consider the quality of the collector and of the installation.

8. Investigate local building codes, zoning ordinances, and subdivision covenants, as well as any special regulations pertaining to the site.

You will probably need a building permit to install a solar energy system onto an existing building. Building code and zoning compliance for a solar system installation is typically a local issue.

Common problems homeowners have had with building codes include:

  • Exceeding roof load

  • Unacceptable heat exchangers

  • Improper wiring

Potential zoning issues include the following:

  • Obstructing sideyards

  • Erecting unlawful protrusions on roofs

  • Installing the system too close to streets or lot boundaries.

Special area regulations — such as local community, subdivision, or homeowner’s association covenants — also demand compliance. These covenants, historic district regulations, and flood-plain provisions can easily be overlooked.

To find out what’s needed for local compliance, contact the following:

  • Your local jurisdiction’s zoning and building enforcement divisions

  • Homeowner’s, subdivision, neighborhood, and/or community association(s)

2. Beehive solar heating systems

Beehive solar heating systems have a solar collector that is an array of black tubes that resemble a beehive. Water from the pool is pumped through the filter and the collector and returned to the pool. These systems raise the water temperature only very little, so they could not be used to replace a natural gas or propane pool heater. These and all other types of small solar pool heaters are not very effective no matter how efficient they are because they do not cover a large area.

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Solar pool heating systems with solar panels for above-ground pools.

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Solar pool heating systems with solar panels for above-ground pools are mechanically similar to solar pool heaters for in-ground pools. They have a filter, strainer, pump and flow control valve. They have a solar collector made of several solar panels, and the water is pumped through the panels after leaving the filter. The existing pump can be used. They do not raise the water temperature as much as solar systems for in-ground pools, per sq. ft. of solar panel, because heat energy escapes from the sides of an above-ground pool through radiation. Nevertheless, with a large enough solar collector, this type of heating system could be used in place of a propane or gas pool heater and save much energy. One manufacturer claims that they can raise the pool temperature by up to 10º, which is a reasonable claim, and that temperature rise may be enough for you. If you install one and it is not sufficient you may be able to add more solar panels.

Appendix B Solar Pool Covers

Solar pool covers, also called solar blankets, are a relatively inexpensive way to increase the water temperature of your pool so that it is heated up in less time. They are similar to bubble wrap; they have two sheets of thin plastic with large, round air pockets. The air pockets give them a high insulation value. Unlike other pool covers, they float on the water’s surface. Clear and light-colored solar pool covers allow solar radiation to pass through them, heating the water, and they trap the heat when the water is warmer than the air. This is what happens in a car on a hot, sunny day. UV radiation passes through the windshield and heats up the car’s interior. Heat escapes as infrared radiation, which is partially trapped by the windshield, so the temperature rises. Black solar pool covers absorb solar radiation to become

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                                                                                                   Solar pool cover material

hot, and some of this heat energy is conducted into the water. They also trap the heat when the water is warmer than the air. Black covers are not as effective as clear or light-colored covers and the evidence is that they are not as widely available. Most of the solar pool covers that are used for rectangular in-ground pools are designed to be reeled in, and they are light in weight so this is not difficult for one person. Those used for round, above ground pools are normally not reeled in. When the pool is covered by a solar pool cover and the pool’s heater is off, the water temperature will be from 1º to 4º higher, depending on how much direct sunlight there is. Some manufactures make much very exaggerated claims about how their covers raise the temperature. Thus, the heater does not run as long to raise the temperature up to the thermostat-set temperature.

Solar pool covers are not always good investments. They may fail too soon, in as little as one year, if the plastic is very thin or if there is much direct sunlight or if it is left in direct sunlight when rolled up (it should be covered or put in the shade when not in use). The plastic decays because UV rays from the sun break it down, even though UV inhibitors are added to it. Most that are designed for in-ground pools cost between $50 and $100. Those designed for above-ground pools cost less. Their prices average about $0.50 per square foot. You will probably also buy a solar reel, for $200 to $300. Solar pool covers should be washed to avoid contaminating the pool with algae, mold, or bacteria. Custom solar covers are available for large or odd-shaped pools, at a higher price.

Solar pool covers are sold in round, rectangular and oval shapes of all sizes. Their thickness, in mils, is the thickness of each of the two plastic sheets. They range in thickness from about 5 mil to 16 mil. For comparison, the heaviest plastic drop cloths are 6-mil thick. The thicker they are, the longer they last but the harder to roll up; their effectiveness is about the same regardless of the thickness. The most popular thickness is probably 12 mil, because these are the thickest covers that are not too hard to roll up for most people. 16-mil thick covers probably are too heavy for some reels, making them sag. Only the thickest sizes have multi-year warranties. If you have much heavy rain or hail, a thicker solar cover will resist weather damage.  

The payback period of a solar pool cover cannot be directly compared to that of a vinyl pool cover, the most popular type of pool cover, because they are normally used differently. A solar pool cover is not a winter cover. It is probably used mainly short term on pools that also have a safety winter cover, and used short term in climates where the pools are used all year around. If you compare it directly to an insulated vinyl cover, because you would use them on the same days, a solar pool cover may have a similar payback period. Insulated vinyl covers probably resist thermal radiation (trap the heat) about as well, and block evaporation as well, and last longer. As explained above, evaporation removes about 60% of the heat energy from a pool when the pool is warmer than the outside air. Many people probably buy solar pool covers because they are mislead by ads that exaggerate the cover’s ability to increase the water temperature, and aren’t aware that the covers do not last long. If you compare them directly, consider that you may use the solar pool cover more often because it is easier to use, and using it more often would save water and energy.

Appendix C Heat Pump Swimming Pool Heaters

Heat pump pool heaters use electricity to transfer heat energy from the air to the water in the pool. They use the same vapor-compression cycle as refrigerators, air conditioners, and residential heat pumps. Residential heat pumps heat the home’s air in winter, and the cycle operates in reverse in summer to cool the home’s air. In refrigerators and air conditioners, this cycle operates in reverse. Water from the pool enters a heat pump pool heater, where it is heated and pumped back into the pool. In the heater, the water flows through a heat exchanger, where energy is transferred to it from a refrigerant. The refrigerant is hot because it was compressed by the compressor as it flowed through the vapor-compression cycle.

Heat pump pool heaters are also called “electric pool heaters”. There is another type of electric pool heater, the electric resistance pool heater, but these are only used for small above-ground pools.

Heat pump pool heaters can be used at any air temperature is above 45 º, but on cooler days they are much less efficient and thus much more expensive to operate. A very large pool can be well-heated with a large heat pump, but most homes don’t have enough extra electric capacity for this.

Models can be roughly compared by their coefficient of performance (COP). This is the average number of units of heat generated for each unit of electricity used. The COP’s of various models range from 3.0 to 7.0. By comparison, electric resistance pool heaters (which are only used for small, above-ground pools) generate one unit of heat for one unit of electricity, which would be a COP of 1.0. The COP is only a rough estimate because not all manufacturers measure the COP’s of their products at the same water and air temperatures. Most manufactures use 80ºF as the outdoor temperature and the pool temperature. You may be given the temperatures at which a COP was computed, allowing you to compare models fairly well. If your existing heater uses gas, and it is 75% efficient (which is typical), and you install a heat pump with a COP of 5.0, for each $1000 you presently spend, you may spend $750 with the heat pump. This depends, on your cost of gas and electricity, and the average outdoor temperature at which you heat the pool.

The smallest models, which are for above ground pools, have heating capacities of about 50,000 Btu and cost under $2000. The largest models, which are for in-ground pools of about 35,000 gallon, have heating capacities of over 120,000 Btu and cost over $4000. An average pool holds about 25,000 gallons.

If you use a heat pump pool heater, hire an HVAC technician to do a tune-up if one has not been done for years. If you install one, hire an HVAC technician periodically. Some technicians who specialize in residential heating and cooling are well-qualified to do this tune-up. In a heat pump tune-up, the key components of your system are checked and adjustments made to keep it operating efficiently. The check may include:

  • Checking if the system has lost refrigerant. If some has evaporated the heat pump will be less efficient.

  • Checking unit for peak efficiency and adjusting if necessary

  • Inspecting the motor and recording the “amp draw”. If the amp draw is too high the compressor is demanding too much electricity, and is wasting energy.

  • Checking for noise that indicates that the motor bearings are worn out.

  • Inspecting the wiring.

  • Calibrating the thermostat. If the water temperature is slightly too high because the thermostat is inaccurate, the heat pump is wasting energy.

The U.S. Department of Energy publishes the estimated costs of heating a pool with a heat pump pool heater in many U.S. cities. Below are the 2012 estimates for four cities. Visit energysaver/articles/heat-pump-swimming-pool-heaters to find the estimated costs in the city nearest you. These tables also estimate the annual heat pump pool heater costs and savings compared to using an electric resistance or a gas pool heater. Notice that the heating seasons differ greatly: 12 months in Miami, 8 months in Phoenix, etc.

Table 1 estimates annual swimming heat pump pool heating costs by location, by water temperature, and with or without using a pool cover.

Table 1. Costs by Location of Heating Outdoor Pools with a Heat Pump












w/ cover










w/ cover










w/ cover










w/ cover





Below are the 2012 DOE estimates of the costs of heating with gas and electric resistance pool heaters.

Table 2. Annual Savings Comparisons of
Gas and Electric Pool Heaters


Annual Cost

Cost w/ 5.0 COP

Heat Pump Savings

Gas Pool Heater





































Electric Resistance





Appendix D Filtration Pumps that Use Less Energy

Most new pools are built with a pump which is sized to pump all the water in the pool through the filtration system in about eight hours. Pool builders instruct pool owners to run their filtration pump six to eight hours each day to keep their pool clean. The cost of energy to operate an average size pump, which is 1 ½ horsepower, for eight hours a day is over $100 per month. This cost varies greatly with the cost of electricity in the state. To reduce your electric costs, when you need to replace your pump, install a smaller pump or a two-speed pump and operate it more hours each day.

According to the “pool pump cube rule”, when you reduce the speed of a pump motor by half, you use one-eighth the power. The flow of water from a pump whose motor speed has been reduced by half will be reduced by only half. Slowing the pump motor to half of the original speed will require you to operate the pump twice as long to pump the same amount of water, but the motor is drawing only one-eighth the power. So one-eighth the power multiplied by twice the time will use about one-quarter of the energy for the same water turnover. In practice, this turns out to be about one-third of the energy use.

Pool pumps that can be set to operate at half speed are called two-speed or low-speed pool pumps. All major manufacturers of pool pumps make them. On their high speed, the motor turns at the same speed as the typical residential single-speed pool pump. On their low speed it turns at one-half of the high speed. The high speed is used when a higher flow is required, such as when using a pressure side pool sweep or using a solar collector on the roof.

Most pool owners do not have a two-speed pump. One reason is that most people believe that larger pumps pump faster, ending the pumping cycle sooner and thus using less energy. The two-speed pool pump is becoming more common on new pools.

Some states provide rebates to owners who replace their pool filtration pumps with two-speed or low-speed pumps. This is proof that operating your pump at a lower speed will lower your electric costs.