Pool Heaters

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How To Determine Proper Pool Heater Size

To best determine the appropriate pool heater for your needs, some basic information about your swimming is needed. With this information and your desired pool water temperature, simple formulas are applied to predict the required BTU's needed to heat the pool water to the desired temperature.

BTU stands for British Thermal Units, a measurement of energy required to raise the temperature of one pound of water by 1 degree in Fahrenheit temperature. All swimming pool heaters are rated in BTU output, and the more BTU's a pool heater puts out the more heat it can produce. Ultimately the larger the pool heater in BTU, the faster it can heat a given amount of water. This is rated as BTU's per hour.

Now to select the size heater required for your needs, we need to determine the surface area of the swimming pool measured in square feet and the amount of temperature rise over average outside air temperature measured in degrees.

1. Surface Area is calculated using the the formulas provided below.

  • Round Pools: radius (1/2 diameter) x radius x 3.14
  • Oval Pools: 1/2 length x 1/2 width x 3.14
  • Rectangle Pools: length x width
  • Kidney-Shaped Pools: length x width x 0.75

2. Temperature Rise  is simply the desired pool water temperature minus the average ambient air temperature. This is very easy to calculate. Say you would like the water temperature to be 80 degrees, and during the coldest month you wish to swim the air temperature is 60 degrees. You would have a maximum temperature rise of 20 degrees (80-60=20).

Now with surface area and temperature rise factored, you can refer to the chart to find just how many BTUs would be required to achieve the desired temperature of the pool water.

Pool Heating Chart


                                         Temp Rise



5 ° 10 ° 15 ° 20° 25 °
Pool Surface Area sq.ft.

                Required Heater Output BTU/ Hour

200 21,000 31,500 42,000 52,500 63,000
300 31,500 47,300 73,000 78,800 94,500
400 42,000 63,000 84,000 105,000 126,000
500 52,500 78,800 105,000 131,000 157,000
600 63,000 94,500 126,000 157,000 189,000
700 73,000 110,000 147,000 184,000 220,000
800 84,000 126,000 168,000 210,000 252,000
900 94,500 142,000 189,000 236,000 284,000
1,000 105,000 157,000 210,000 263,000 315,000




Choosing The Best Pool Heater For Your Application

The questions range from which brand is best to what type of pool heater is best for my application. The answers vary as there are many factors that go into determining the best pool heater for your swimming pool or hot tub. Since this is a fairly large topic, we will have to break this down into several blogs to sort it out and get the information in here. So let us start with the basic types of pool heaters and their best applications.

Solar Pool Heaters work by using the sun’s energy to heat pool water as it passes through panels or tubes typically placed on a rooftop. Your existing pool pump circulates the pool water through the panels for heating, then back into the pool. This is a fairly economic way to heat the water if the location of the pool and panels are right. Because the average BTU’s of a solar pool heater are limited, they work best year round in southern climates with much sunshine. Cloudy or rainy days will definitely reduce the heat output of these units, but a few sunny days in a row and the pool water will warm back up again. Pools in northern locations should use another form of heating their water as solar panels have little effect during the cooler months.

Gas Heaters And Propane Pool Heaters work by burning fuel within a chamber and transferring that heat to the pool water. The use of a natural gas heater or a propane heater will require a storage tank for propane, or a natural gas line hookup. Gas or propane heaters have the highest BTU rating and work great in any climate. They are the quickest at heating up and maintaining warm pool water temperatures. Although very effective, pool heaters of this type can be costly to operate daily or over extended periods of time. Great for quick heat ups for short periods.

Heat Pumps are often referred to as electric pool heaters. These pool heating systems work by absorbing energy from the outside air and compressing it. This compression of air causes heat, which is then transferred to the pool water. Heat pumps are great at maintaining pool water between 80-90 degrees all year. Because the cost of electricity is less than the cost of natural gas or propane, heat pumps are cheaper to run on a regular basis or for long periods of time. The downside of the heat pump is they become ineffective in cooler climates or temperatures below 45 degrees. Regardless of which pool heater is best for your application, a good solar blanket or thermal pool cover is needed to help keep the heat in the pool water. I hope this short blog helps sort out the basic differences between pool heaters and their applications. For more on pool heater sizing, please read our other blogs on the topic. Thanks again for reading.

Making The Most Of Your New Pool Heater

  • Size your Pool Heater appropriately. Remember a pool heater can never be too big, but a pool heater can be too small. A larger than needed pool heater will heat the water faster and spend less time running. This can save on wear and tear maintenance costs.
  • Maintain proper water chemistry. PH is probably the single biggest problem pool owners face with regards pool equipment like heaters. Low pH levels (acidic) will cause corrosion, high pH levels (base) will cause mineral deposits that could potentially clog your pool heater's plumbing, reducing water flow and efficiency.
  • Maintain correct water flow rate. Cleaning your cartridge or back-washing your sand filter will ensure maximum water flow through the heater and improve efficiency.
  • Protect your pool heater investment. The use of a pool heater cover will reduce the heater's exposure to the elements.
  • Give your pool heater plenty of room. Allow appropriate clearance around the Pool Heater as recommend by the manufacturer.
  • Gas pressure adjustment is critical. This ensure safety and maximum efficiency of your new pool heater. This should be performed by a PROFESSIONAL before using the heater.

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