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How cold is too cold to use my heat pump?


The main advantage of purchasing a heat pump is that it allows you to extend your pool season. You can even enjoy the pool in the winter months. This is especially helpful if you live in an area where temperatures drop dramatically during the winter. You may ask “How cold is too cold to use my heat pump?”

In this article, we will answer that question, and provide some information to help you get the most out of your unit.

Heat Pumps

A “heat-only” pump designed to only heat the water and not cool it can work effectively down to the lower 40s. However, the ambient temperature greatly affects the ability of air-source heat pumps to produce heat. The colder the air, the less heat your heat pump will be able to produce. You can extend the lower temperature limit for your heat-only pump by winterizing it when the temperatures drop.

Reversible Units

Some units, like the AquaCal ICEBREAKER®, are “reversible” and provide heating or cooling. Reversible units can also operate when the outside temperature is down to the mid to lower 20s. However, that does not necessary mean it can heat the pool to 80° on a 20° day. As a rule of thumb, the highest water temperature rise you can get from an air-source heat pump under ideal conditions is 30°. For example, if the outside temperature is in the 40s, you can expect the pool to warm up only to the 70s.

Commercial Heat Pumps

Not many heat pumps can handle the demand of heating commercial swimming pools. Although can install several residential heat pumps to create enough BTUs to heat any size pool it may be inefficient. There is, however, a reversible unit on the market that could create almost a half a million BTUs with just one heat pump: The Great Big Bopper (GBB). To read more about the GBB, please click here.

There are also geothermal heat pumps that are produced for commercial applications. For more information on geothermal heat pumps pool heaters, click here.


These options will help you enjoy your swimming pool even in the colder months. Just bear in mind the limitations of your unit as indicated by the manufacturer. This is the most important step in helping it run efficiently and without being damaged. Next time you ask yourself “How cold is too cold to use my heat pump?” remember there are options.

Regardless of the when Old Man Winter decides to visit, you can extend your swim season beyond…well…swim season!

If you have any questions, please do not hesitate to ask us, or leave a comment below.

This Post Has 43 Comments

  1. I live in Kissimmee, FL and we have an Aquacal heat pump. Whenever the air temp gets into the low 60’s it tries to heat but immediatley cuts out. Typically I am only trying to heat the hot tub at this point. Mid 60’s and higher it works well on both the pool and the hot tub. Is there an easy way to check the air temperature sensor?

    1. Hi Steve,
      Typically, when the ambient air temperature drops into the 50’s, the unit will start icing up and go into defrost mode. You should see FS or “unit defrosting” on the display. Did you notice any messages? If you would like to discuss this over the phone, please call us at 727-823-5642.

      AquaCal tech support

  2. Hello! We have just turned on the heat pump and are running the pump continuously to allow the water temp to rise. We usually run the pump for 8 hours a day (10am-6pm). Does the AquaCal have a flow meter to determine if the pump is running? If not will the heat pump be trying to heat the water even when there is no flow after 6pm? Will that damage the heat pump.

    1. Good Afternoon Mr. Hermanns,
      Hope you are doing well. The heater does have an internal water pressure switch that should shut the machine down when the circulation pump stops.
      I would call the factory at 727-523-5642 On Monday Morning to troubleshoot further & set up service if needed.
      If you notice the heater running with no water flow, please turn off the breaker that supplies power to the machine.
      Robert Brown
      AquaCal Tech Support

  3. I live in Central PA and have a heat pump for my in-ground pool with the temps dropping into the 40’s is it ok to leave my heat pump on to continue to heat our pool till the end of September? The pump does get frost on it.

    1. Hi Debbi,
      Heat pumps will start to ice up with air temperatures in the low 50’s and 40’s. They will spend more time defrosting themselves than heating your pool. It’s best to run the unit when air temperatures are above 60 degf, typically during the day, and cover the pool with an insulated blanket overnight to minimize heat loss.

      AquaCal Customer Support

  4. Good morning. I live in upstate New York and I am interested in adding a heat source to my pool beyond our current solar setup. Realistically, we are only looking to heat from early May – late Sept. How realistic is it to expect a mid-80’s pool with a heat pump? Thanks.

    1. Hi John,
      It is certainly possible. It depends on the size of your pool and the size of the heat pump. There are many heat pumps in upstate New York. We have a sizing program on our website to estimate what size unit you would need for your pool. If you have any questions, or need assistance, please call us at 727-823-5642.


  5. My current pool is between 79-83 (I live in South Florida) how much would I expect that the heat pump would get the pool up to? I was hoping to get the pool up to 86 and keep it there.

    1. Hi Jason,
      There are many factors involved to heat your pool to 86; size of the pool, size of the heat pump, wind conditions, do you use a blanket at night, etc. We have a sizing program on our website that can help determine what temperature can be achieved. Please call us at 727-823-5642 and we will be happy to assist you.


  6. Will I be able to heat a spa pool (13×30) combo in the colder months specifically at night in Cape Coral Florida? What temperature can I expect to get the spa to during those months at night considering it does go down into the 40s and dips into the 30s here and there?


    1. Good Afternoon Robert,
      Hope you are doing well. We do have special units called IceBreakers that are able to keep heating when temps get in the mid to low 30’s.
      However, you must keep in mind that when heating a larger body of water such as a pool, you can only expect to get a 30 degree rise above ambient air temps.
      On smaller bodies of water such as spa’s, you can achieve a greater heat rise and get to decent bathing temps. If you have additional questions, please feel free to call us at 727-823-5642.
      Robert Brown
      AquaCal Tech Support

  7. Out here in southern california it gets really hot during the summer, but during the winter its not comfortable to go in the pool. Thanks for informing me a little bit more about how I can enjoy my pool during the chilly season, which is almost here by the way. Thanks!

  8. I have a the Icebreaker model SQ 156R. We have been having temperatures in the teens at night and not getting above freezing during the day. It’s 24 degrees now and I turned the heater to a set point of 40 degrees. The Mode indicates “Heat” but it’s not heating. Is there a minimum temperature for the heater to run? Thank you

    1. Hi Mike,

      Heat Pumps operate best with warmer ambient air temperatures, i.e. high 50F’s and over 60F, because it uses the ambient air as its heat source. When you run a heat pump at 24F it will start icing up and go into defrost mode to melt the ice. At 24F the unit will spend more time defrosting than transferring heat to your pool. If you have any questions, please call us at 727-823-5642.

      1. Hi !
        We live in Pa. overnight temps around 40
        We haven’t used our pool yet – every time we turn heater on, it ices up so we turn it off. I keep arguing to just leave it on and let it defrost / run it’s course. Please help us stop fighting over this. Is it a mechanical issue or is the air too cold ?
        Also do we leave heater on if temps drop to 28 next week over night ? So confused. Thank you !

        1. Good Morning Ms. Donal,
          Hope you are doing well.
          The issue with the heat pump frosting up will depend on what type of heat pump you have.
          If the unit is a for heating only, then it should not build clear ice.
          It should sense when ambient air temps are too low for it to run & shut itself down.
          If the unit is a heat/cool unit, it will run in lower ambient air temps and build up some frost.
          However, the unit should reverse its refrigerant flow to melt off the frost.
          If the unit is building up clear ice & not reversing to defrost itself, then there is an issue that needs to be resolved.
          Please feel free to call customer support at 727-823-5642 for additional guidance.
          Robert Brown
          AquaCal Tech support

      2. …and yet on your website it says the heat pump will work even in cold weather. Ours definitely stops working when it hits 61 degrees F.

        1. Hi Tracy,

          In general, heat pumps will transfer heat with air temperatures above 60 DEGF. If the unit is shutting down at 61 DEGF, please call us at 727-823-5642 so we can help troubleshoot.

          AquaCal Tech Support

  9. Great service ……on time and very polite service person Josh Fort. He explained the concern and made the correction…… this is a very customer driven company. I recommend them very highly. Ask for Josh. He is great.

  10. I just purchased a house with this awesome piece of equipment; the water is quite cold; how long does it generally take to heat average size pool. Thanks so much for your time.

  11. Live in coastal Connecticut and had an icebreaker installed on my 17,000 gallon gunite last season. My pool faces south but i was able to maintain 80 F degree water until the end of October. I started loosing efficiently due to evaporation in early Oct but starting using a liquid solar cover which drastically decreased the evaporation and improved efficiency.

    My experience is exactly as this Aquacal states, if ambient temperatures are above 40 F and wind or evap arent a factor there are no problems heating and maintaining temperature.

    At the end of October, we started having nights below freezing. The icebreaker will automatically defrost and then start hearing again but the efficiency is too low to battle temperatures in CT that late in the season.

    However, i can maintain 80 to 90 F water from begining of May to end of October by extending run time and using liquid solar blankets. If it works for me in CT, should work in most places where folks own swimming pools!

  12. Hi, I have an Aqua Cal heat pump installed in Mexico city. For 2 years the heat pump was working ok. But since october of last year the heat pump has been freezing . The supplier has checked several possible reasons, they even change some parts and they are trying with an other location with more space, air and sun.

    Now that the heat pump is in the new location the heat pump is not able tho warm the pool more than 77F / 25C.
    Its impposible to achive a decent temperature. And just start to freeze again. The supllier told us part of the problem is the cold months.

    The temperature in these days 48F – 76F. / 9C – 24C.

    Could this be a reason for the problem? Ist been so long since the heat pump start to fail so the pool is now closed.

    1. Hello Selegna,

      A heat pump can start icing when run in lower ambient air temperatures, i.e. 40’s & 50’s DEGF. However, they are designed to defrost. Once the defrost cycle starts and the ice is melted they should go back to heating. Does the heat pump eventually melt the ice on the unit? Are you running the heat pump 24 hrs/day? During the warmest part of the day, does it look like the heat pump is raising the pool temperature? If you would like to contact us directly to discuss please call us at 727-823-5642 or send your contact information to

  13. I have an indoor 10,000 pool, the room is 20×40 with 30 foot ceiling sloping to 8 feet. If i put the heat pump in this room, wont it just take the heat that has escaped from the pool and put it back into the pool?

    this room is not heated by a furnace, removing the cover from the pool heats the room up very fast !!!

    1. Good afternoon Andrew-

      Running the heat pump indoors may actually cool the room down. The air coming off the fan during operation is 9-12 degrees colder than the ambient temperature. Proper CFM airflow and ventilation are important for an indoor installation. If the air off the fan isn’t vented out of the room, the colder air will begin to recirculate through the evaporator reducing BTU output and if there isn’t adequate airflow across the coils it may cause an LP error code. Contact the factory at 727-823-5642 for more information regarding indoor installations.

      Hope this helps!

    2. This will work, and will also dehumidify, but it will pull down the room temp down, so the heatpump will perform like it’s in winter! So have max ventilation in the room to stop it pulling out all the heat energy. So the room might get colder than ambient!

    1. Good afternoon Dave-

      There are a number of factors to consider when heating a pool so the answer to this question will vary depending on the circumstances. Generally speaking, if the night time lows are in the 50’s & 60’s and inclement weather isn’t a factor(wind, rain, cold fronts, etc.) you shouldn’t have any problems achieving an 80 degree water temperature.

      Some factors to consider when heating in these temperatures would be your geographical location, the duration of the cooler temperatures, runtime of the pool circulation pump, blanketing, if the unit has a hot gas defrost and the temperature rise you are trying to achieve. The cost estimator program on our website can help determine if you will be able to heat the pool in a particular month and location. The program uses the average monthly temperatures from weather data compiled over the past 30 years and covers the United States as well as many international locations. Once a city and state are selected the monthly temperatures will populate. The temperatures in red indicate the month(s) that the unit will not efficiently heat. The program does not take indoor installations, solar or a gas assist into consideration and is based on a typical outdoor installation. The months shown in black indicate the average temperature is conducive for heating. Since the estimator program is based on averages, spikes in weather conditions cannot be factored in.

      If you need more detailed information on heating please contact Aquacal technical support.

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