how to size a pool heater

Sizing Your Pool Heater

32 thoughts on “Sizing Your Pool Heater

  1. I had a Heat Pump for my 24′ round. The guys at the pool store said it was the right size. Nope!
    1. My pool mostly in the shade due to the tree cover.
    2. I’m on a cliff with a clear path to the beach (Revere Beach in MA).
    3. Always windy.

    Existing heater cost about 3k. The next size up cost 7k. Did the solar cover, to much stuff form the trees would fall including animals.

  2. The key part of the article is about gas consumption. A smaller heater will burn longer to get the desired temperature rise, a larger heater will get that the pool to temperature faster. Roughly the same amount of gas will be consumed either way, so don’t assume that the larger one will cost more to operate.
    Spa combos almost universally have a 400K btu heater.
    If considering adding a heater, do not forget to consider the price of running the gas line to it. That expense has been a deal killer on many heater installations.

  3. I am in southeast GA. I recently put a (roughly 14k to 15k gal) pool in. 15×30, 3.5′ at shallow, 7′ at deep end. Rough estimates on day light temperatures are 60 degrees. I am looking at a heat pump due to this, but… according to BTU calculator, Hayward does not offer a large enough heat pump… HELP!!

  4. After reading the information maybe I missed something but I didn’t see information on ELECTRIC HEATERS.
    Please advise,

    1. Electric pool heaters are not very common because of their high unit and operational cost. Even the smaller electric heater can pull 100-125 amps on single phase circuits. But most of the electric pool heaters require a three-phase power source, another rarity in residential installations.

      But the main reason for them not being included was their rarity. But Coates has a sizing calculator.

  5. Hello there.
    How do I calculate the BTU needed for a pool 640 SQF pool that has solar blanket and Solar heating panels, and its in Los angels, California, full of sunshine days.
    I need to boost the heat only to extend the swimming season and rise Temp to 85′ from April, May, June and November .
    TNX for your help!

  6. What factors should I consider if I have an indoor pool? the poolhouse is heated so I won’t get the quick variations in ambient temp to cool my pool? My pool is 15k gallons unsure of the dimensions…


  7. I have a typical 15 x 30 pool & spam combo. Had a 400k BTU LP heater so the gas install is in place. Live in central Florida, no screen enclosure. Pool temp is fine for 8+ months of the year. Never used the heater for pool, too expensive.

    I just want a replacement LP heater, electronic ignition, decent quality, for the occasional spa use only. What would you recommend?

  8. I recently purchased a 350000 BTU Hayward universal heater for my 18 x 36 inground pool. upon looking at my gas meter it only has 3/4 inch piping and the chart says that I should have at least one and a quarter inch all the way to the heater. Do I need to get a new gas meter or can I just go up to a one and a quarter inch all the way to the heater and then reduce it back to 3/4 in at the heater inlet?

    1. Likely you solved this but make sure the 3/4″ isn’t the pipe going into the gas meter the pipe going from the meter to the pool needs to be larger.

  9. I just purchased 400,000 btu hayward heater. I have run
    90 feet of 1 inch natural gas pipe to heater and reduced it at last 4 feet to 3/4 inch. I may be undersized on pipe. How will that affect heater performance?

    1. You’d be starving the heater of gas, so obviously it is not good for performance. Think about what your car do if you cut the gas supply to a fraction of what it needed?

      Hayward’s LowNox heaters require a 1-1/4″ gas line for a 50-100 foot run.

  10. Hi,

    I have a 31 x 31 x 5 pool (in ground)
    Windy conditions
    Ambient temp of 65 F
    My pump runs 6 hours a day
    2 ppt of salinity
    My target temp is at least 86 F

    How many BTUs should I be looking for ?


    1. I see you have most of the info we asked for in the article to get the BTU size. I do not see the area of the country you live in, the seasons you’ll be operating the unit or the cost of utilities.

      If you can provide that information, I can try to calculate the answer. You may also use the Raypak Sizing Calculator we have linked in the article.

  11. Hello. I have a 18 x 33 ft above ground pool that I use for exercise. Due to my medical conditions I can’t tolerate water temp less than 85-86 but in southern PA, (in the summer) I am lucky to be able to get in the pool more than 10 days. I will be using propane as can’t afford connection gas fee. In order to be able to swim all summer (and end of spring plus beginning of fall would be wonderful!) I would need anywhere from 5 to 15 degree increase, depending on the day/night. Can you tell me what btu heater and also, any recommendations of what heater. Unfortunately, being a disabled widow, cost is a concern for me, so if any ideas of heater with that in mind. Thank you very much for any help you can give me!

    1. Don’t see an answer so I will as a poolman I’d install a Starite 333 or 400. In my experience the Starite’s are the longest lasting heater.

      1. In our experience, Sta-Rite is the most costly to repair and tend to be overdesigned. There are a lot of moving parts in a Sta-Rite heater; a la, a lot that could go wrong. I generally prefer Raypak because their heaters are relatively simple, and they are a company that specializes in heaters. Because the parent company is Rheem, when you call Raypak you ae guaranteed to get someone who knows their way around a heater and can tell you how to troubleshoot any problem. With the larger pool companies like Hayward or Pentair, you may call about a heater issue, but you are on the line that is more familiar with pumps or filters and can only go through basic troubleshoot handbook.

  12. Live in SC & have inground pool, 34’ by 15’. Shallow end is 3ft & deep end is 6ft 7 in. Would like to heat to 85 degrees & want to use April – October. Have a poly gal roof over it. What brand heat pump do you recommend & how many btu’s? Don’t want to urs propane or gas heat. Thx for feedback.

  13. I have a 36×20 pool in NY surrounded by trees and shade. I don’t have gas line and want to use a heat pump.
    Which size do you recommend?

  14. Matthew —
    Your information here is great, and it sounds like you really know your stuff… So, I have a question on the same subject of pipe size/length and btus. We are in an older home that had gas heater removed prior to our moving here a few years ago. In deciding which heater to buy as a replacement, as our northern CA weather is great in the summer but very cool at night (and in winter months) I wanted to go with the “bigger is better” concept primarily for efficiency. Also, I’m thinking we should go with 400 btus as we don’t have a cover (the pool is kidney shaped). It measures approx 25 x 40, and we’ve tried a solar cover but that’s a real pain.

    Contractor A said that for a 400 BTU Jandy and a gas line run of approx. 90ft, we would need to upgrade the existing 3/4″ line to 1/1/4″ pipe — same as what the Jandy chart above (and our brochure) states. So we upgraded the pipe, re-ran the line, etc. and now have a 1/1/4″ line — but we haven’t yet pulled the trigger on which heater we want.

    When I learned that our regular pool service provider also installs pool heaters (which I didn’t realize until recently), I requested a bit from them as well. They/Contractor B carry Raypak and Pentair — not Jandy. And in working up a bid, they said they would need to put on a line reducer, as both Raypak & Pentair take a 3/4″ gas line!!! Imagine that! Something just doesn’t make sense to me…

    I haven’t yet received Contractor B’s bid, but I don’t recall them measuring the long distance for the gas line, and wonder if they simply don’t factor that into the equation. To me, this would mean that a 400btu heater would be starving for gas…

    I would very much appreciate your input, as my knowledge of pool heaters and gas lines is very new and very limited — but my sense of logic tells me that Contractor A has done his homework.

    Thanks so much!

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