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How Does a Water-Source (Geothermal) Swimming Pool Heat Pump Work?

Customers often come to us at AquaCal because they are trying to determine whether a water-source heat pump is a good investment. This is certainly understandable because water-source heat pumps embrace newer technology, and therefore are less popular than other types of heating systems. So in order to address this subject and to help others, we have decided to discuss water-source heat pumps in this article.

A water-source swimming pool heat pump, also referred to as a geothermal heat pump, transfers heat from a water-source to your swimming pool water. Source water enters the unit and passes over an evaporator coil, which contains a cold liquid refrigerant, often referred to as “Freon.” As the source water passes over the coil, the refrigerant heats to become warm Freon gas. The source water cools, exits the evaporator, and travels back to the water-source. The warm Freon gas passes through a compressor, which compresses it to hot Freon gas. Then, this hot Freon gas passes through a condenser, which is where the pool water enters and exits the unit. The pool water washes over the coil, heats, and leaves the unit warm. As heat transfers from the coil to the pool water, the hot Freon gas cools to once again become cold refrigerant, and the process starts again.

Because many types of bodies of water exist, many types of water-source heat pumps exist. Some common water-source systems are explained below.

  1. Open loop: Also known as a deep ground well, an open loop consists of two deep wells: one that supplies water to the heat pump and one that returns water back to the ground. How can you tell if your well is deep enough? The bottoms of deeps wells should be within porous rock-based soil. By contrast, the bottoms of shallow wells are typically within sandy soil. A shallow well is subject to rapid draw down and clogging from loose soil.
  2. Closed loop: Also known as a ground loop, a closed loop system uses the ground as the heat source, rather than the water itself. In this system, plastic tubing is placed underground. A mixture of water and glycol (an antifreeze) circulates through the tubing and collects heat from the ground. The heated mixture returns to the heat pump to heat the evaporator coil. A closed loop system can be either shallow and wide (called a horizontal closed group) or deep and narrow (called a vertical closed group).
  3. Surface water: A surface water system is a type of open loop system. This system draws water from an open body of water. Keep in mind, however, that higher maintenance is required to keep the water-to-refrigerant heat exchangers free of fouling from organic materials. Either fresh water-sources or salt-based water-sources can be used. We do not recommend salt-based water-sources because barnacles and sea mussels can clog the plumbing system and cause a need for equipment replacement.
  4. Mechanical loop: This water source is part of a large system that uses water to remove heat from a commercial air conditioning system. As the air conditioning system removes “waste” heat from indoors, it transfers it into a water loop. This loop is then cooled using a rooftop cooling tower. A water-source heat pump helps the air conditioning system operate more efficiently by tapping into this loop and removing this “waste” heat from the air conditioning system.
  5. Water-source heat pumps can also be used to transfer heat from unheated swimming pools to spas. Because of the large size of a swimming pool, you can transfer enough heat from a swimming pool to warm a spa without noticeable decreasing the swimming pool’s temperature. Specifically, you can use a 50°F (10°C) swimming pool to warm a spa to 104°F (40°C).

Advantages of Water-Source Heat Pumps

A water-source heat pump only uses electricity to transfer heat, rather than to create heat. Water-source heat pumps are therefore very energy-efficient, and AquaCal customers love energy efficiency! The efficiency of a swimming pool heater is measured by its coefficient of performance (COP). The COP of a heat pump generally measures between 5 and 6, which translates to an efficiency rate between 500% and 600%.
Other advantages of water-source heat pumps include: low operating costs, longer lifespan, quiet operation, flexible location (can be installed indoors and outdoors), and small environmental footprint.

Disadvantages of Water-Source Heat Pumps

Water-source heat pumps have few disadvantages. Prominent disadvantages include their high purchase costs when compared to gas heaters and their slow heating.

So now you know how a water-source heat pump works. If you have any questions about what type of water-source heat pump is best for you, leave a comment below or contact AquaCal directly. We would be happy to help!

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This Post Has 32 Comments

  1. Where to find this type of pump? i am really looking for one and i want cheap cost solution.please reply me with some link where i can buy this pump.Thanks

    1. Hello Dominick,
      To purchase a heat pump you will need to go through a dealer. Dealers can be found on our website under the “Where To Buy” tab. If you have any questions please call us at 727-823-5642.

    1. Good morning, we would gladly help your friend over run times and set up of their unit to optimize performance and help with operating costs, please provide us with a phone number or email address and we can have someone in the area contact them.

  2. what are the conditions to utilize geothermal heat pump close loop? actually, i have a villa located in Dubai and i need to heat and cool the swimming pool water via geothermal heat pump close loop type.

  3. Will a closed loop geothermal heat pump work year-round in the lower NY/upper NJ area where the pool is enclosed in a retractable enclosure? (see Wells or trenches would be dug. Which method is better? Please confirm that the unit can be placed in the basement. How many BTUs would be necessary to warm to water to 80 – 82 degrees?

    1. Good morning Mike-

      Geothermal heat pumps transfer heat from one body of water to another as compared to air to water which is how a standard heat pumps operates. The bodies of water can vary greatly from jobsite to jobsite. You can go to the link on our website… and enter the information for your geographical area to get a better idea of what to expect.

      Before a geothermal unit is purchased, a questionnaire is filled out and reviewed by an experienced team of professionals who work in conjunction with the local Aquacal sales representative and installer to ensure the site will meet the necessary requirements.

      To calculate how many BTU’s are required to heat water to 80-82 degrees, The starting water temperature is subtracted from the desired temperature to get the number of degrees needed to raise the temperature and then multiplied by the pounds of water in the pool for the total BTU’s required.

      There is additional information for the geothermal units on our website at and If you would like to provide more detailed information, please contact technical support so we can help.

  4. The people of HVAC training have cooperation between HVAC learning encountered as a successful combination. The presence of both theory and practice was enriching, especially when you consider looking at the business with the loupe in your own business.

  5. We are building a home with a geo thermal heating and air conditioner…… my question is can we use the same system to heat both the house, pool and spa?

    1. Good afternoon-

      An AquaCal Geothermal Heat Pump can be used to heat both your Pool and Spa. It can share the same water “loop” or supply well as the home heating and air conditioning unit. (Depending on the type of “source” water that you will be using.) It is critical for your installer to calculate the load and properly size the closed loop or supply well before purchasing or installing your equipment.

      Please feel free to contact us should you have any further questions.

  6. Hello was wondering if geo thermal water source heating is more cost effective then aqua cal heat pumps for a 50k pool in west palm beach fl?

  7. Good morning Ranger and thank you for your question-

    Within the state of Florida, we offer a factory direct Preventative Maintenance Program. This is performed by our Factory Service Team. Outside of Florida, we don't have factory techs (other than the Northeastern US), but most HVAC companies can perform a Preventative Maintenance Inspection on the systems. In regards to the water source, you may need to contact a well company if the water source is from a well point. If the water source is from some other source (cooling towers, lakes, ground coils), you would be best to contact the installing dealer for preventative maintenance.
    For the most part, there is little maintenance needed to ensure proper operation of the Geothermal heat pumps. We hope this answer your question, please feel free to contact us should you need further assistance.

    1. Good afternoon and thank you for your question. A home heat pump may not be suited for the chemicals maintained in a pool, much less if the water chemistry is not maintained properly (such as with high chlorine levels, or improper calcium hardness, pH, and/or high Total Alkalinity levels). These can corrode the heat exchanger if the water chemistry is corrosive, or can calcify if the water chemistry is scale forming. However, the basic principle of a heat pump would dictate that the pool water is large enough so as to allow a home heat pump to operate properly. However, consider that the discharge from the heat pump is opposite of what you would want in your pool.That is, when it's hot out and you want to cool your home, the discharge from the heat pump will be warm/hot water. You wouldn't want your pool to be hot. Then, when it's cold out, and you want to heat your home, the discharge from the heat pump will be cold water…thus making your pool even colder. We hope this answers your question, please feel free to leave any feedback or contact us directly if not.

      1. Someone else should answer questions on these blogs even if that means there not the author of the responded to post. Although you eventually acknowledge the question, in the prior answer the passage of weeks still has it being ignored as it's been misconstrued.
        At the same time you've apparently dropped the price on your largest air source true (reversible) heatpump by five figures, by over a third, from one online retailer so it's cost per BTU is lowest of any model perhaps ever sold by you at least. It however wastes the heat extracted unlike water source units.

        Researching this recently was very depressing. Sub 100% combustion units sell for just as much as your most expensive model and use over half dozen times- probably seven, 8, or NINE times as much 'energy.'

        If your half million BTU unit uses a single compressor, then you need to make a methane combustion cogenerating model that is designed to make structural (high stackable) block ice while it generates grid parallel and islandable in outage power. In the summer it's true there is a surplus of low grade heat available but there are industrial processes that can be brought poolside not just extra floors dug to store ice for summer all year round architecturally.

        A company already doing this- using invertor's to avoid local red tape and drive down the road paved by unstainable in cost presently still fuel cell's and PV.

        The present parking underground in many buildings is wasted space now that people don't need to park car's at all, and they can instead store themselves on the road when not transporting anyone who summons them- the question has been for decades, what are we going to use all this garage infrastructure for? Now we know! TO store the ice that's a waste product of removing heat from water all winter long!

        I am a rare member of the public who sees your about twenty thousand dollar price tag as a great bargain. It's a real proof of concept. Now you need to take it further, partner with an invertor generator AND driven motor company that will allow you to capture just the additional electronics heat, OR as I implore you stop referring to combustion for heat only as 'gas'- rather USE gas instead of coal or worse, directly, and capture the heat of combustion coal etc. currently 'vents' as waste on the coldest day of the winter, on every day, as if to maximise the loss of polar caps, as if they work for the shipping industry, or some warm water ocean dwelling scum bucket society.

        Work for us please.

  8. Cornelia, yes, a heat pump can heat both your swimming pool and your spa. Please take a look at our blog titled "How to Heat a Spa/Hot Tub with a Heat Pump" for more information, feel free to post any other questions, we will be glad to help!

  9. We are building a new home and installing a Spa pool. Our home is also geo thermal. Can we simply use the heat pump that is being installed to heat the spa? Or do we need to purchase additional attachments?

    1. Cornelia your phrasing appears to met to have masked your real question and I hope priority. Many hours after reading and even responding myself (see next question) I realized you essentially are asking for what in the 80's Carrier would of called a THP5 with some other letter's perhaps to denote geoxchange as you say your using for the domestic space and pottable water warming if not heating.

      What I realized is that pool thermal water conditioning is seen from a desert half full perspective- instead of 'don't worry about too much brocoli it's good for you or "pool's need not be wasted in the winter[/summer] one" or to use your word "not a mere accessory".

      For me a house in any climate that has outdoor temps that very from what we want indoors substantially needs not just dumb mass, or even engineered waxy styrene wall panels that melt and solidify just slow enough to stagger night and day delightfully. No, what's needed is a place to put excess heat, or get it. So if by "we" you mean including yourself as more then a bystander, but as designer, then yes, the answer is likely you will have to deal directly with core technology companies to assemble the system needed as if your the first/only person ever to need a house.

      The good news is that it's not just 3d printing that's new- but teams of engineers no longer being needed to innovate. The cahllenge i hope someone will aspirre to is somewhat trivial in fact.

      It's a good science fair project for a team of junior high kids, or one upperclassmen or homeschooled elementary school summer fun. There are tables, or software that knows how much water your pool will need to store day heat for night, how big the pumps will need to be, whether c02 or helium and taht sort of thing- but it is very doable and it's the right way to get the cover of many digests documenting your heroics- as that's what they are.

      There half million btu pump can remove heat quickly before a summer morning swim not just so the pool is cool to our touch so that it better absorb all the heat as it leaks back into the house all afternoon.Any real pool is only going to show a fraction of the water below- water that in inexpensive not wading pools below can be kept even hotter or cooler- in fact enough ice made in winter to take all summer to melt.

      The reason we don't see this standard is because any good use of land is oppressed from consumer's knowledge. If you have any yard, then you have no need for utilities, and can profit from it greatly, but at tract home builder's profitablity.

      Companies like Aquacal resist mainstreaming fearing real competition. They like there products being sold installed for three to ten times as much as they receive from local contractors for them. Your money- smart money- does not give them the same sadistic thrill as ripping off a token few fools does.They forget all the courts or really ours, the ball is never there's to direct, and finally, the internet, will let the game server us as it always should.

  10. What a great information provided by you on heat pumps.. Thanks for sharing such fabulous post with us….. Waiting for your next post… Keep writing…

  11. Water source heat pump is a good system for the pool users, now a days people want the variety type of use of the pool in different season. The heat pump used for the transfer of heat from the water source to the swimming pool water, this type of system very useful for the users and the owners also.

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