What Size Pool Heater Do I Need?

If you’re thinking about installing a pool heater, you might be wondering what size you need. Here’s a quick guide to help you choose the right size heater for your pool.

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Selecting the right size pool heater is essential for maintaining a comfortable swimming environment. There are a number of factors to consider when making your decision, including pool volume, desired water temperature, and climate.

Pool volume is the primary determinant of heater size. Most manufacturers provide sizing charts that list the recommended heater size for pools of various volumes. For example, a common rule of thumb is that a 100,000 BTU heater is adequate for a 400-gallon pool.

Water temperature is another important factor to consider. If you live in a climate with cool winters, you will need a larger heater to maintain your desired water temperature. Conversely, if you live in a warmer climate, you may be able to get by with a smaller unit.

Finally, it’s worth mentioning that there are two types of pool heaters: electric and gas. Electric units are typically more expensive to operate but are easier to install. Gas units are less expensive to operate but require more installation work.

How to Size a Pool Heater

Determining what size pool heater you need can seem daunting, but it doesn’t have to be. There are only a few factors you need to consider, and we’ll walk you through them all here. In this article, we’ll cover everything you need to know about sizing a pool heater.

Consider the climate

If you live in an area with year-round warm weather, you won’t need a pool heater at all! But if you find yourself shivering in your swimsuit come autumn, a pool heater will allow you to extend your swimming season well into the cooler months.

There are a few factors to consider when sizing a pool heater, including:
-The size of your pool
-The average temperature in your area
-How often you plan to use your pool

Once you’ve considered these factors, you can start to narrow down which type and size of heater will best suit your needs.

Determine the pool’s volume

The first step to sizing a pool heater is to determine the volume of your pool. You can use the following formulas to calculate the volume of your pool:

Rectangular Pool: length x width x average depth x 7.5
Round Pool: diameter x diameter x average depth x 5.9
Oval Pool: length of long side x length of short side x average depth x 5.9

The results of these calculations will be in gallons. Once you have the volume of your pool, you can move on to the next step.

Calculate pool surface area

To calculate the surface area of your pool, simply multiply the length by the width. If you have a kidney shaped pool, you will need to calculate each section separately and then add them together.

For example, a pool that is 20 feet long and 10 feet wide has a surface area of 200 square feet. If the pool is also 6 feet deep, it has a volume of 1,200 gallons (200 x 6).

Now that you know the surface area of your pool, you can calculate the BTUs needed to heat it.

Consider the pool’s usage

When trying to determine what size pool heater you need, the first thing you should consider is how you will be using your pool. If you only plan on swimming for a few months out of the year, then you will not need as large or powerful a heater as someone who plans on using their pool year-round. For example, a heater that is meant to heat an entire Olympic sized swimming pool will not be necessary for a small backyard pool.


Now that you know the ins and outs of pool heater sizing, you can be confident in your purchase. Be sure to take into account the factors we discussed—pool size, desired water temperature, climate, and fuel type—to ensure that you buy a heater that will keep your swimming pool at the perfect temperature all season long.