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How Can I Size My Swimming Pool Heat Pump?

A common question that consumers ask us at AquaCal when shopping for swimming pool heat pumps is: “How big does my heat pump need to be?” You should have a trained swimming pool professional size your swimming pool heat pump, as its size will depend on many factors. There are, however, general formulas we provide to our customers to approximate heat pump size. We explain how to use these formulas in this article.

Heat pumps are sized according to required BTU (British Thermal Unit) per hour of the swimming pool. Consumer often make the mistake of purchasing under-sized units – units with insufficient BTU output per hour. Under-sized units must run longer in order to heat swimming pools. These longer run times translate to decreased efficiency and higher operating costs. Use the following instructions to approximate the BTUs per hour your heat pump will require.

  1. Determine your desired water temperature in °F.
  2. Determine the average air temperature of the coldest month during which you plan to use your swimming pool in °F.
  3. Subtract the average air temperature from your desired water temperature to calculate the required temperature rise.
  4. Calculate the surface area of your swimming pool in ft2:
    1. Circular pools: radius x radius x 3.14
    2. Kidney-shaped pools: length x width x 0.75
    3. Oval-shaped pools: (0.50 x length) x (0.50 width) x 3.14
    4. Rectangular pools: length x width
  5. Calculate the required BTU output per hour: surface area x temperature rise x 12

In addition to these instructions, we at AquaCal provide our customers with a free cost estimator program. This program takes only minutes to complete and will provide you with recommendations on the size of heat pump you need to efficiently heat your swimming pool. To access this free program, click here. If you need additional help, one of our dealers will be happy to assist you in determining the right size heat pump for your swimming pool! Click here to find a dealer nearest you.

By following these steps, you can quickly and easily approximate your required heater size. Remember, however, that only a licensed swimming pool professional can perform a proper sizing analysis! If you have any questions or concerns about heat pump sizing, feel free to leave a comment below or contact us at AquaCal directly.

This Post Has 38 Comments

  1. I would like to purchase a Sunblazer heat pump from Aquacal just to heat my in-ground spa. The dimensions are 6×6 round and the water depth is 3 feet. What size heat pump do I need to get a 15 degree rise within a 30 minute period?
    I live in Jacksonville, Fl

    Thank you.

    1. Hi John, That’s around a 300 gallon spa. If you are in the Jacksonville area and wanting 104 degree water in 15 minutes during the winter, you may want to consider using or supplementing with a gas heater. The Sunblazer can heat 300 gallons of water from 78 degrees to 104 in about 30-40 minutes with the air temp in the 70’s. 55 degree water to 104 will take over an hour.
      Hope this helps.


  2. Just purchased a 80,000 btu heat pump and it looks like it has to be plumbed with 2” piping, but when I look at my filter it is 1 1/2” pipe do I need to change all the pipe to 2” thanks

  3. I never took into account that the size of your pool would determine what size of a pool pump you need. My friend actually has a pool, but her pump is old an need to be replaced. These tips could really help her get the right size of pool pump, so thank you for sharing them.

  4. Hi,
    I leave in Cape Coral and have a 400sqft in ground pool with a 4.5′ average depth and approximately 13,500 gal. I would like to have my water temperature at 80 degrees F in the coldest month which is January. What Aquacal heat pump would you recommend? BTW I use Aquablanket.

    Thank you

    1. Good Aftenoon Mr.Bunje,
      Hope you are doing well. With the size of your pool & the use of the Aqua Blanket. I can recommond the SQ125 or the T115.
      Both will work very well on your pool without being oversized. I show that each would need about 5-6 hours of run time to keep the water at 80 degrees during the colder months.
      Robert Brown
      AquaCal Tech Support

  5. I have a 17′ x 34′ kidney custom shape inground pool. About 500 sq ft and 17k gallons. I live in Connecticut. Plan on using the pool May to Oct and keep pool about 84 degrees. Will the T115 work?

    1. Hello Frank.
      Based on the information provided (we actually had to input using the pool from the middle of May to the middle of Oct based on your desired temp) the T115 will work if you use an insulating blanket on your pool. If you are not planning to use a blanket, we recommend the T135. If you have any questions please call us at 727-823-5642.

  6. I have a 35″ x 22 in ground pool.
    I would like to heat the pool to 80 to 85 degrees
    What size Heat Pump should I purchase?

  7. I need to replace my Pentair heat pump for my spa with a surface area of 115 sq ft.(3.5 ft deep) located in Phoenix, AZ. Will the largest Pentair Ultratemp Model 140 (50/63/80 BTU/COP 88,000/4.0) heat the spa faster than the calculator recommended size of Model 70 (50/63/80 BTU/COP 50,000/4.0)? I want to heat the spa as fast as possible to 100F when the outside temperature is around 50F.

    1. Hello Robert,

      A larger BTU heat pump will heat the spa faster. You may not be able to heat the spa to 100F when the outside air is 50F. As a rule of thumb a heat pump will heat the water 30F above the ambient air temp. For example, if the air temp is 50F you can expect to heat the spa to 80F, under ideal conditions.

  8. I’m installing a 12 x 26 pool with 5 x7 spa. Pool avg depth is 4′. Located in Soithwest Florida. Pool installers recommended SQ125 but I’m not sure that is large enough to heat the spa very quickly on 55-60 degree evening. Should I install SQ225 or is that overkill for approximately 10,000 gallons?

  9. What size heat pump pool heater do I need for a 12’x30′ inground pool? We live in West Palm Beach, FL. Where the average temperature is 75 in the winter.

    1. Hello Shirley,

      Assuming your pool has an average depth of 4.5′ and a total volume of 12,150 gallons, our SuperQuiet SQ125 would be sufficient to heat your pool. With our Tropical line the T90. If you have an further questions please call us at 727-823-5642.

  10. what size heat pump pool heater do I need for a 14′ x 28′ inground pool, between 1450 and 1500 gals of water, we live in central pa

  11. I have a 9000 gal , salt water pool and leave in Texas. How much BTU is recommended and what is a good approach to getting a bigger BTU then recommended . Is it a waste of energy and money ? Please advise . Thanks

    1. Hello John,

      Which Texas city do you live in? A larger BTU heat pump will draw more electricity, but will heat the pool/spa faster….so it will not run as long. We have a sizing/cost estimator on our website to give you an idea of how much it will cost to operate the different size heat pumps. Please call us at 727-823-5642 if you need assistance.

  12. Building a new pool and need a recommendation on hearter size.. I’m not sure how many gallons but it’s 92Lnft/ 466 surface and it’s 17’6″ x 31’6″
    Live in S. Florida

  13. We have an inground pool, measured at approx 12,000 gallons. A dealer recommended the Heatwave SQ166R. We live in AZ with temps in the "cold" part of the year (late Oct-late April) in 50-60 avg daytime and 30's-40's overnite. Will that unit be about right?

  14. My pool is approximately 12 x 18, and is said to be 10,000 -11,000 gallons. Using the calc above, It seems that a 108,000 BTU pump is appropriate. My thought is that I would buy the 115,000 BTU heat exchanger as this would run more efficiently and heat the pool faster in cooler weather. Am I on the right track, or is the larger motor going to waste energy?

    1. Good morning Andrew-

      A 115,000 BTU heat pump should work properly, you are definitely on the right track! you can send your email address to, there are other factors to keep in mind when choosing the right size unit for your swimming pool and we would be happy to walk you through it!

      Have a great day!

      1. hi Matt,
        Hope you are doing well. You are missing a few steps.
        12 w x 18 l = 216 sq f
        216 sq ft x 10 ft average depth = 2160 cubic feet
        2160 cubic x 7.5 gallons per cubic ft = 16200 gallons
        16200 gallons x 8.3 lbs of water per gallon = 134460 lbs of water
        1 btu raises 1 lb water by 1 degree F
        134460 x 12 degree rise + 1,613,520 btu's needed

  15. Thank you Garry- we would also encourage anyone that has any doubts on the correct sizing to check out our "Heat Pump Operating Cost Estimator" found in this website, it would help you find the correct heat pump for you!!

  16. For getting the more comfort people use the heat pumps in their pool. Generally heat pump used in the size of the pool and as per the temperature you can use the pump. There are variety type of pumps available in the market by any sizes, in the winter season generally the pumps used and as per the pump capacity the current consumption also needed.

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