What Size Pool Heater Do I Need?


Living in the Sarasota area means that you’re able to enjoy your pool virtually year-round, especially if you have a pool heater. While a heater is an excellent investment for many pool owners, choosing the right size can be a bit of a challenge.

If you choose a heater that’s too small, you’ll likely find that it simply can’t keep up, leaving you with less-than-ideal water temperatures. On the other hand, bigger isn’t always better. A pool heater that is too large for your needs will burn unnecessary energy, which can get expensive.

So, how do you decide which sized pool heater is right for you? Here are a few important things to consider.

Factors That Influence Pool Heater Needs

The size of your pool is one of the most important factors that influence your heater needs. This includes both the volume of water it holds and its surface area, since a larger surface area leads to more evaporation.

In addition, you’ll want to consider how warm you like to keep your pool, the lowest expected temperatures during the months when you expect to heat your pool, and how quickly you want it to heat up. If you have a built-in spa, you’ll need a larger heater than you would if you were heating a pool alone.

Those who enjoy swimming at night or want to use their pools during the colder months can also benefit from sizing up when choosing a pool heater. If you have a pool cover or a solar blanket, you may be able to achieve the desired effect with a smaller heater, since they hold in heat and make it easier for the heater to maintain your desired temperature.

Pool Heater Size Estimates

Now that you’re clear on some of the factors that influence your heater size needs, let’s look at a simple calculation that will allow you to easily estimate your minimum pool heater size.

1. Start by calculating the surface area of your pool by multiplying its length times its width.

For example, a pool that is 15’ by 30’ has a surface area of 450 square feet.

15’ x 30’ = 450 square feet

2. Divide the surface area by 3 and multiply the result by 1,000.

This will give you the minimum BTU size you need to heat your pool. Continuing with the example above:

450 sq. ft. / 3 = 150
150 x 1,000 = 150,000 BTUs

Don’t forget that this is the absolute bare minimum. In most cases, you’ll want to choose a heater that is at least one size larger to ensure it heats your pool quickly and maintains your desired temperatures. Also remember that if you want to maintain higher temperatures or heat your pool in cold weather, you’ll need a larger heater.

The following chart reflects some general guidelines for gas pool heaters. Size yours up or down depending on the factors discussed above or consult an expert for a more specific recommendation.

Pool SizeRecommended Heater Size
16 x 32 feet250,000 BTU
18 x 36 feet325,000 BTU
20 x 40 feet400,000 BTU

Still Not Quite Sure? Our Experts are Here to Help!

With so many variables to consider, choosing the right-sized pool heater can feel a bit overwhelming – but don’t worry! Our pool installation experts are here to help. When you order a custom pool from Swim Inc., we’ll make sure you have everything you need, including a perfectly sized pool heater. Contact us today to schedule a consultation.

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