Pools come in all shapes and sizes, and so do pool heaters. This means that selecting the right size is necessary for heating your pool efficiently. The heat output of heaters is measured in British thermal units (BTUs), and, when looking for a heater, it is important to look at its output BTU.

Deciding How Much BTU You Need

In order to calculate how long a particular heater will take to heat up a pool, there is a simple formula to use: weight of water in the pool times the temperature you want to raise it. This will tell you the amount of output BTU you will need to heat a pool to the desired temperature in 48 hours. The amount of need BTU may vary depending on environmental and geographical factors such as elevation, but this is a good general guideline. Note that the weight of a gallon of water is around 8.33 lbs, so multiply the number of gallons by 8.33 to find the weight of the water in the pool.

Determining the Output BTU of a Heater

Many heaters will only list the input BTU, which is the amount of energy they take in. This is not the same as the amount of heat energy they produce (output BTU). To find the output BTU of a heater from its input BTU, you just need to multiply the input BTU by the heater's efficiency. Efficiency should be listed as a percentage by the manufacturer. In many cases there will be a list of specifications relevant to the pool heater, either on the website if you're shopping online, or somewhere on or near the pool heater if it is in a store. Though some advertisements will explain specifications in paragraph format, must are set up as a list that might look something like this: Measures 32" high by 13" wide by 26" deep 80 percent efficiency electronic spark ignition copper heat exchanger 100,000 BTU stainless steel burners 1-year Warranty In that list, the information important to sizing is the 80 percent efficiency and the 100,000 BTU. In general, BTU listed like that will be input BTU, but if you are unsure of whether it is input or output BTU, you should contact the manufacturer to find out. So, to find output BTU for the example pool heater, you would multiply 100,000 by 0.8 (80 percent converted to decimal). In this case, the output BTU would be 80,000. Note that the U.S. department of energy requires all pool heaters to have at least 78 percent efficiency. Many higher end pool heaters will have an 85 to 90 percent efficiency rating.

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