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Swimming Pool and Spa Heater Information

Sizing and Definitions

Sizing Chart: How much Pool Heater do you need?

Remember when selecting a pool heater that these are just recommendations. You can always size down from the recommended heater - but this will mean that it will take longer for your heater to heat your pool to the desired temperature and longer running times can mean more costly energy bills. On the other hand, you can size up from the recommendation which will mean you pool/spa will heat faster and the shorter running times will mean more savings on your energy costs!  Also, you should take into consideration your pool environment. If you live in a naturally warm locale, the recommended size or smaller may work for you just fine. If you are in a colder climate, you may want to consider going with a slightly higher BTU heater.  Also, are you heating just a pool, or are you also heating a spa?  If you are heating a spa, you may want to invest in a larger heater so that you spa can be heated to optimal temperatures quickly for use.  Here is a chart to help you decide which heater would be appropriate for your pool situation.

Size HeaterGallons in PoolSq. Ft. Surface Area of Pool
100 - 200 BTU heaters1,000 gals to 10,000 galsUp to 300 sq ft
200 - 300 BTU heaters10,000 gals to 20,000 galsUp to 500 sq ft
300 - 400 BTU heaters20,000 gals to 40,000 galsUp to 800 sq ft
400 BTU heaters40,000 gals to 80,000 galsUp to 1200 sq ft

Calculate Your Pool's Water Volume

In order to figure out proper doses of chemicals for your pool, you need to determine how many gallons of water it holds. To do that, you need to know four different numbers: the length, width, average depth, and a multiplier that determines gallons.  Here is the formula:

Length * Width * Average Depth * Multiplier = Gallons

Determine the Multiplier:

Rectangle, square, or free-form pool:multiplier = 7.5.

Round or Oval pool: multiplier = 5.9

Determine the Average Depth:

To determine the average depth in a pool where the bottom slopes, measure the shallow end, the deep end depth. Add them together and divide by two (2).

Example: Shallow End = 2'. Deep End = 10'

2' + 10' = 12'; 12'/2 = 6' Average Depth

Standard Pool Above Ground Pool Sizes with a Pool Wall of 48 inches
12 ft Round~ 2,975 gallons12' x 24' Oval~ 5,948 gallons
15 ft Round~ 4,646 gallons15' x 30' Oval~ 9,293 gallons
18 ft Round~ 7,646 gallons16' x 32' Oval~ 10,573 gallons
21 ft Round~ 9,106 gallons18' x 33' Oval~ 12,267 gallons
24 ft Round~ 11,895 gallons  
27 ft Round~ 15,054 gallons  
30 ft Round~ 18,585 gallons  
33 ft Round~ 22,488 gallons  


Standard Pool Above Ground Pool Sizes with a Pool Wall of 52 inches
12 ft Round~ 3,398 gallons12' x 24' Oval~ 6,797 gallons
15 ft Round~ 5,310 gallons15' x 30' Oval~ 10,620 gallons
18 ft Round~ 8,602 gallons16' x 32' Oval~ 12,084 gallons
21 ft Round~ 10,408 gallons18' x 33' Oval~ 14,019 gallons
24 ft Round~ 13,594 gallons18' x 40' Oval~ 19,116 gallons
27 ft Round~ 17,205 gallons  
30 ft Round~ 21,240 gallons  
33 ft Round~ 25,700 gallons  


Standard Pool In-Ground Pool Sizes with Varying Depths





12' x 24'






14' x 28'






15' x 30'






16' x 32'






18' x 36'






19' x 38'






20' x 40'






22' x 44'






25' x 45'






25' x 50'






30' x 50'






General Information and FAQ's

Pool and spa heater information can sometimes be hard to decipher.  Here are some commonly used heater terms along with explanations of what they mean and how they apply.

Natural Gas versus Propane - What should I use?

The type of gas your pool heater uses is very important and needs to be determined before your pool heater is purchased. The type of gas used should be determined depending on which area of the country you are located and what is available and affordable in your area. Consult your gas company to find out which is most efficient for the pool heater you are interested in.

Cupro Nickel Tubing - What is it and why is it important?

Cupro-Nickel is an alloyed metal.  It is used in heat exchangers to add strength and corrosion resistance.  It is comprised of Copper and Nickel usually at a ratio of about 90% Copper and 10% Nickel.  If the heater is installed in an area known for hard water, (above 25 Grains of Hardness per Gal.), the use of cupro-nickel tubes in the heat exchanger can allow for the flow rates to be accelerated to scour the tubes and help prevent scale build up. 

Here is what Cupro Nickel tubing looks like:

ASME - What does it mean?  And what does it mean to ME?

A.S.M.E. stands for American Society of Mechanical Engineers. This group has laid out certain design criteria that would protect it’s industry and insures that products meets all ASME standards. Here’s a brief look at how this applies to your heat exchange:  All materials used in the manufacturing of an A.S.M.E. Heat Exchange, copper finned tubing (the ASME copper finned tubes are thicker than the standard copper finned tubes used on residential pool heaters), tube sheets and even stud bolts, are brought into the manufacturer and held for inspection by a State Inspector. This inspector charges the manufacturer for inspection visits.

The inspector will come in several times per week to review all the materials, data reports, etc. proving that all products have met rigid A.S.M.E. standards.  Once the materials have passed inspection, the heat exchange assemblies are water pressurized, up to 260psig. and then the exchanger is closely inspected by the State Inspector.  Once all tests are performed and the exchanger has passed the tests, the inspector will sign off on the Data Reports, which are then filed at National Board, who retains records of all ASME boilers and pressure vessels.

Some states or counties may require the use of A.S.M.E. heat exchangers in all commercial pool heaters. ASME heaters are held to a higher quality standard and have endured more rigorous testing prior to shipment.

What is a Polymer Header and is it important?

Polymer is basically a plastic.  It is very light, tough, and non-corosive.  The benefits of polymer headers are a lighter unit for installation, durability, and rust free performance.

Here is what  a Polymer Header looks like:

Electronic versus Millivolt Ignition - How do I know which is right for me?

Pool Heaters sometimes have the option of having an electronic or a millivolt ignition. The difference between the two is the pilot light used to heat the swimming pool. The millivolt ignition pool heaters use a constant pilot light. The good thing about millivolt ignition is that no electrical work is needed. The bad thing is that if there is a high wind situation, the pilot light will blow out and needs to be relit manually.  Additionally, there is a small amount of energy lost while the pilot light is always burning and the warmth from the pilot light can attract rodents or other pests seeking heat.

The electronic ignition is considered a more modern option for a pool heater. These type of pool heaters need an electrical hook up. The ignition turns on and off the pilot light only when it is needed. It is a more efficient way of heating your pool as there is not a pilot light constantly using a small amount of energy, and it negates the possibility of attracting pests with it's warmth.

Some pool professionals feel that millivolt heaters are easier to work on and have little experience working on electronic ignition pool heaters.  As older millivolt heaters are replaced with electronic ignition heaters, this will eventually change and millivolt heaters will be considered old technology.

Pool Heater versus Heat Pump - What is the difference and which one is right for me?

Most people choose to use a standard pool heater for their heating needs.  A gas pool heater (Natural or Propane) is a fairly efficient and convenient way to keep your pool or spa at the optimal temperature; however, some people choose to use a heat pump instead.  Gas pool heaters use burners to create heat and make your water warmer.  On the other hand, heat pumps do not generate heat, they simply capture it and move it from one place to another.  If you live in a warm climate, a heat pump may be a great option for you.  If you live in a colder climate, a heat pump might not be a good option.  Also, if you are heating a spa, even in a warmer climate, a heat pump may not be able to heat the water to 102 degrees or keep the temperature up as well as a gas powered heater.

Heat pump pool heaters cost more than gas pool heaters, but they typically have much lower annual operating costs because of their higher efficiencies. With proper maintenance, heat pump pool heaters typically last longer than gas pool heaters.

Below is a diagram that shows how heat pumps operate:


Compare this to the chart below of how a Gas Pool Heater Operates:


If you have more questions or need assistance in selecting the heater that is right for you, please contact our pool and spa heater experts at 1-800-544-3730!


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