Sizing Your Pool Heater

Step 1: Calculate your Surface Area (Pool Length x Pool Width)

When you are determining which size pool heater to buy, the first step is calculating your pool’s surface area. A lot of pool owners assume that you use your pool’s gallon size to determine your heater size. In fact, there are some websites that DO use the number of gallons. If you have a pool with a large surface area, the heat has more space to escape and subsequently, more water to heat. As a result, the heater needs to be large enough to compensate for surface area and the pool size.

To calculate the surface area of your pool, multiply the length times the width.

For example: If your pool is 15 x 30, then your surface area is 450 square feet.

Step 2: Divide the Pool’s Surface Area by 3

The pool’s surface area divided by three gives you the minimal BTU size recommended for that particular surface area. Continuing the example above with the 15 x 30 pool, after dividing by 3, you get 150. Therefore, the minimum size heater that is recommended for a 15 x 30 pool is 150,000 BTUs.

This is simply the recommended minimum size. I always go higher. Especially when it comes to gas heaters, you always want to oversize the unit. The job of a pool heater is to replenish the heat loss at the surface of your pool. Most heat loss happens overnight. Without a solar cover, there is no way to make up for the loss. That’s when having a higher BTU size comes in handy.

Step 3: Consider Your Variables

Before deciding, consider all the variables that may affect the efficiency of your heater such as owning a solar cover, climate, and how often you use the pool.

For a 15 x 30 pool without a solar cover, I might recommend the 250 k or 300 k BTU model, depending on the customer’s preferences. That way it accounts for heat loss, evaporation, and unexpected windy conditions. It also accounts for pool owners who prefer to swim at night.

By adding a solar cover, you’re changing the game. Using a solar blanket in conjunction with your heater is the best tag team in terms of providing the best heat in the shortest amount of time. With a solar blanket, you might not need a 300 K BTU heater. You might settle on the 200K or 250k heater. Sometimes, it’s cheaper to simply invest in a solar blanket than paying for a larger heater.

Residential Gas Heater Sizing Calculator

Raypak has a gas heater calculator that configures your city and state with your desired water temperature, average air temperature, and desired temperature rise. Raypak’s online calculator allows pool owners to input specific information about their pool and location and configure what size heater is best, not only for their pool but taking your physical location into consideration as well.