What Size Swimming Pool Heater Do I Need?

cold pool water pool heatersFinding the right heater for your pool can be hard work. Normally, bigger is better as it will warm the pool faster. However, this also means you will use more power depending on how oversized the heater is.

There is a bit of simple math to be done, as well as a few other considerations. Let’s take a look at the factors to consider in accurately identifying the right size heater for your pool.


The first step to finding out the right pool heater is by identifying your pool’s surface area. Here is a simple example to give you information to find your own.

You want to multiply the length by the width, so if the pool is 15 feet by 30 feet, that gives you a surface area of 450 feet.

Now that you have the surface area, you want to divide by 3, giving us 150. This is the first step in calculating how many BTUs (British Thermal Units) your pool will need. Next, add three zeros to the 150, gives you 150,000 BTU. this is the correct sized heater we need for this pool.


Before we go and find a 150,000 BTU heater, we have to consider a few variables:

  • Where do you live, and what is the climate like?
  • How often do you use the pool?
  • Does the pool have a cover?
  • What materials are the pool made out of?

Each of these variables has some influence on the amount of ambient heat your pool is already exposed to without the work of a heater.
For instance, if you have a solar pool cover, this means you can use a lower BTU heater, as they work hand in hand.

Likewise, if you plan to use the pool at night more often than daytime, you face the task of reheating water that was warmer in the sunlight.
You also want to consider if your pool is inside or outside, as the air temperature can also have a positive or negative effect on the pool’s temperatures. This variable also influences how efficiently the water gets heated.

For information about professional pool care, see our Pool Maintenance service page.


Finally, you want to choose what method of heating you use. Between gas, electric, and solar methods, a gas heater is the quickest, but also the most expensive.

A electric heater is the cheaper option, but is also slower. This is due to an electric pump only being able to move so much water at a certain flow rate, at a certain temperature.

The last option being a solar pool heater, is great if it’s a hot sunny day. But otherwise it is low on the scale of efficiency, as it is dependent on the relative exposure of sunlight. Obviously this method would be less effective in the winter, and likely not an option for indoor pools unless you’ve got a sunroof installed.


Choosing the correct size and type of heater for your swimming pool is important to optimize efficiency while avoiding excessive utility costs. If all of this seems a bit daunting, you can reach out to professionals to help you make an informed decision.

Click here for a free service estimate from Sun Valley Pool Service!

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