A swimming pool heater allows you to start swimming earlier in the year and stay out in the water a little later in the season. Usually the heater is installed after the pump and filter system are in place. Following are the main types of pool heaters:
These are currently the most common choices. In recent years, energy efficiency for these heaters has nearly doubled. They’re a good choice for pools that aren’t used on a regular basis because they heat the water quickly.
Unlike other heaters, they maintain an even water temperature even if the air temperature fluctuates. They typically last about five years. Oil-fired heaters are often used in more-remote areas where natural gas is unavailable. See more about gas swimming pool heaters.
Heat pumps, which use electricity, cost more than double the price of gas units but use a lot less energy and last longer. They work best in warmer climates where the air temperature remains above 45 or 50 degrees Fahrenheit because they borrow warmth from the surrounding air in order to do the job. They capture heat and move it from one place to another, but they don’t generate heat.
These are growing in popularity and in efficiency. They cost a lot initially—usually between $3,000 and $4,000 to buy and install—but have very low operating costs. According to the EPA, they last longer than gas or heat pump heaters—usually from 10 to 20 years with proper maintenance—and can provide a payback in seven years or less depending on local fuel costs.
If you’re interested in this option, it’s a good idea to have your site evaluated. If you do decide to go solar, have a qualified solar thermal systems contractor install your system. See more about solar swimming pool heaters.
It’s best to have a pool expert ultimately determine the size heater you need because there are so many factors that go into the calculation. These include the surface area of the pool and the difference between the average air temperature in your region and your desired water temperature. In addition, wind and humidity levels and nighttime temperatures can have considerable impact. For instance, if you live in an area with high wind speeds, low humidity, and cool nights, you will need a larger heater.
To minimize energy consumption, use a pool cover and choose a high-efficiency heater whether you’re purchasing a gas heater (see Swimming Pool Heaters: Gas) or a solar heater (see Swimming Pool Heaters: Solar).
Calculating Gas Heater Size
To roughly calculate the size heater you need, you can plug a few numbers into a formula. The first number is the pool area in square feet. Then you need a couple of temperatures—the water temperature you prefer and the average air temperature for the coldest month you will be using the pool. Subtract the air temperature from the water temperature to get the “temperature rise.”
Now, plug these numbers into the formula to find the BTUs per hour you need your heater to generate. The formula is: Pool area x temperature rise x 12 = BTUs needed per hour. How much energy you need is based on an increase of about 1 degree (or a little more) in water temperature per hour with the wind by the pool at 3.5 miles per hour.
Calculating Solar Heater Size
How would you make this calculation for a solar heater? It’s a little more complicated because in addition to the factors mentioned above, your site’s solar potential and the solar collector’s efficiency also come into play.
Ultimately, you need to consult a solar-system contractor. But, as a ballpark figure, the surface area of your solar collector needs to be 50 percent of the surface area of your pool if you’re in a sunny climate and 100 percent if you’re in a region with less sun. The solar collector needs to increase in size if you want your water to be warmer and if you want to lengthen your swimming season. For instance, in a sunny climate like Florida, a solar collector might need to be 100 percent of the pool’s square footage to accommodate year-round swimming.