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Sizing Your Heat Pump Pool Heater

Learn how to size your swimming pool heat pump so that you can get the right size heater for your pool.
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The most important thing about purchasing a pool heater is determining the correct size for your above ground pool.

Determining the correct size will save you money as a pool heater with the correct amount of BTUs will limit the overall run time and reduce your electric bill throughout the season. More importantly, throughout the colder months when you would like to use your heater the most, you will shorten the overall heat time of your pool and in turn also limit the amounts of electricity required to run the unit.

Pool Heaters

The Pool Factory is your source for quality swimming pool supplies at the lowest prices. Whether you’re looking for equipment or accessories for your pool, we have everything you need to take care of every aspect of pool maintenance and care.

Aquapro Eco 550 heat pump

It is also important to know that there is a difference between a electric heat pumps and natural gas or propane heaters. Natural gas and propane heaters require a higher amount of BTUs for comparing to the same size pools.

Look for your pool size below on the Heat Pump Sizing Chart to find the correct amount of BTUs for your pool.

Rules For Sizing Your Heat Pump Pool Heater

  • Size at 4 BTU’s per gallon or 1 BTU per litre of water. To heat in normal summer conditions when ambient air temperature average 70°F in a 24 hour period.
  • Size at 5 BTU’s per gallon or 1.3 to 1.5 BTU’s per litre of water. To heat in normal spring and fall conditions when ambient air temperature average 60°F in a 24 hour period.
  • Size at 6 BTU’s per gallon or 1.5 BTU’s per litre of water. To heat in normal spring and fall conditions when ambient air temperature average less then 60°F in a 24 hour period.

We recommend the use of a pool cover during chilly periods.

Heat Pump Sizing Chart - Above Ground Pools

Pool Size (Feet)Summer
4 BTU's
Spring & Fall
5 BTU's
6 BTU's
Up To 10,000 Gallons
Up To 21' Round or 15' x 26' Oval
50,000 BTU50,000 BTU65,000 BTU
Up To 13,000 Gallons
Up To 24' Round or 15' x 30' Oval
50,000 BTU65,000 BTU85,000 BTU
Up To 17,000 Gallons
Up To 27' Round or 18' x 33' Oval
65,000 BTU85,000 BTU110,000 BTU
Up To 21,000 Gallons
Up To 30' Round or 18' x 40' Oval
85,000 BTU110,000 BTU125,000 BTU

Heat Pump Sizing Chart - Inground Pools

Pool Size (Feet)Summer
4 BTU's
Spring & Fall
5 BTU's
6 BTU's
Up To 10,000 Gallons
12' x 24'
50,000 BTU50,000 BTU85,000 BTU
Up To 15,000 Gallons
14' x 28'
85,000 BTU85,000 BTU110,000 BTU
Up To 20,000 Gallons
16' x 32'
85,000 BTU110,000 BTU125,000 BTU
Up To 25,000 Gallons
18' x 36'
110,000 BTU125,000 BTU150,000 BTU
Up To 30,000 Gallons
20' x 40'
125,000 BTU150,000 BTUSee Dealer

More BTU’s means more power, more heat transfer, quicker results and less operation time.

Pool Heaters: Gas Heaters vs. Electric Heat Pumps

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Keep your pool warm this summer with one of our pool heaters. Here you can learn about the different types to help you make an informed decision.

An Introduction to Pool Solar Heat Covers

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A pool solar heat cover is one of the most cost effective ways to keep your pool at a comfortable swimming temperature, learn how to properly use a cover.

  • March 4, 2015 at 3:54 PM
    Richard H. Trebour

    Tom, I have a 16×32 Oval pool 4ft deep. Partially in the ground. I am looking for an electric pool heater. Which one would you suggest?

    Partial sun in my yard, as far as hook up would I need both a plumber and electrician?

    • March 9, 2015 at 3:07 PM

      An important factor that most consumers overlook when choosing a pool heater is the time of the year that the heater will be used. If you are looking to simply take the chill out of the water on a cool summer night, the correct size heater would be different than if you wanted to extend the swimming season into the late fall. A 16×32′ above ground pool will have approximately 12,000 gallons of water. For general in season use we would recommend a 65k BTU Heat Pump for your pool.

      If you would like to extend your swimming season into the colder months we would recommend a larger 95k BTU Heat Pump unit

  • March 23, 2015 at 10:01 AM
    Karen Gage

    Tom, I have a 24 round completely above ground pool, 5 ft deep, and I would like to buy an electric pool pump heater. We live in Illinois and can only swim late June to end of August. We have a good solar cover, but would like to extend our time in the pool. It has to be electric. Can you help? Thanks.

    • March 23, 2015 at 10:05 PM

      Hi Karen,

      Your pool will hold approximately 16,000 gallons of water. To extend the pool season in a colder area, we would recommend over sizing the heater for your pool size. An AquaPro 112,000 BTU Electric Heat Pump would be perfect to solve your problem: https://www.thepoolfactory.com/aquapro-pro1100-112k-btu-electric-heat-pump.html

      Another option for you…
      Please take a look at the following page with all of our Heat Pumps: https://www.thepoolfactory.com/pool-supplies/pool-equipment/pool-heaters/electric-heat-pumps. The AquaPro Eco500 (top left corner) is rated for up to 16,000 gallons of water which will be sufficient for your pool for general use, like taking the chill out of the pool water on a cool summer night or slightly extending the swimming season. To extend the swimming season into the early Spring or late Fall we would recommend a larger unit.

  • April 18, 2015 at 10:38 AM

    I have a Calorex AW910ALX, which has let me down every yea & ha so ever seemed that efficient. I have a 20k+ below ground pool. What size and make would you suggest for a heat exchange pool heater on a single phase. Happy to go higher on the BTU.

  • April 28, 2015 at 11:19 AM
    John Paul

    Tom, I have a 20′ x 40′ in ground pool that holds between 30,000 and 33,0000 gallons. I live in NY and am looking to extend my pool season from Early May to late September. I have decided to go with a pool heat pump, but I am having a difficult time determining what size I should purchase. I am looking at a Hayward HP21404T, a Heat Siphon Z700HP a Jandy JE3000T or a Pentair Utlat Temp 140C. I am open to other suggestions, but any information would be helpful. We do use a solar cover to help keep the heat in.

    Are any of the ones on your website adequate that I can consider?

    JOhn Paul

    • April 29, 2015 at 3:02 PM

      Hi John,

      Considering your pool size and location, you would need a very large heat pump, at least 130k-140k BTUs. Heat pumps above 140k BTUs can jump quite a bit in price. There are a few professional style heat pumps on the market from 160k-180k BTUs but these will cost double the price of a 140k unit. Since you only want to extend your swimming season from May thru September we would recommend an AquaPro 137k BTU Heat Pump:


  • May 3, 2015 at 2:26 PM

    I have a 25,000 gallon in-ground pool and am looking for the best pump heater… any recommendations?

    • May 6, 2015 at 12:09 PM

      Hi Heather,

      Any model 110,000 NTU or larger would be sufficient for a 25,000 gallon pool. If you would like to extend your swimming season into the late Fall or early Spring or if you live in a colder area we would recommend over-sizing the heater to a 125,000 BTU or larger unit.

      Please take a look at the following link to view our available Electric Heat Pumps.

  • May 8, 2015 at 6:32 PM
    Joseph Franco

    I have a 30′ x 15′ x 54″ above ground pool. The swimming pool is in the shade from 2pm through the rest of the day. What electric pool heater would you recommend? Thank you.

  • May 16, 2015 at 1:45 PM

    I have a 20,000 in ground pool what size BTU unit I need for pool

    • May 22, 2015 at 1:40 PM

      Hi Ray,

      We would recommend at least an 85,000 BTU heat pump for a 20,000 gallon pool. If you would like to extend your swimming season into the late Fall or early Spring or you live in a colder area we would recommend a larger unit like the AquaPro 112,000 BTU or AquaPro 137,000 BTU models.

  • June 4, 2015 at 9:03 PM

    Hi Tom, we just brought a home with an inground 18 X 36 pool approx 21,000+ gallons. We live in KS and would like to use the pool from May to September, the pool is shaded from about 3pm to end of day. It appears the previous owners had a heater that was removed at some point. I assume it was removed likely due to cost. What is your recommended size/BTU pump and best make/brand of pump we should consider. We are new pool owners, do you have any idea of the average increase we should expect to see in our electric bill? Also, we are in the middle of repairing our pool.

    • June 12, 2015 at 11:17 AM

      Hi Julie,

      An 18×36 inground pool will usually hod more than 21,000 gallons (unless your pool is very shallow). With an average depth of about 5′ your pools’ capacity will be approximately 25,000 gallons. After measuring the average depth of your pool you can use our pool volume calculator to get the actual water capacity of your pool.

      Taking your location and pool site into consideration and assuming you have a typical 25,000 gallon 18×36 pool, we would recommend an AquaPro 137,000 BTU heat pump.

  • June 9, 2015 at 11:49 AM
    Alana S

    Hi Bob! We have a 12 x 16 oval pool and are looking for a propane heater for it. We are in New York and want the heater just to take the chill out od the water for the summer months. Which would you recommend? 105K BTU? and How much propane would we need?

    • June 12, 2015 at 11:32 AM

      Hi Alana,

      Please first check local codes for propane use in your area. Some municipalities do not allow propane use for pool heaters. Yes, a 100,000 BTU gas heater would be large enough for a 12×24 pool for summer use.

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