To get an appropriate size electric pool heater, it is important to know the size of pool and the amount of water that needs to be heated. Determine the area of your pool by calculating the length multiplied by the width.

On the Other: Desired Water Temperature

Based on the region the pool is located, the desired temperature of the water may vary. In colder climates, a temperature of 80 degrees will take a stronger heater to warm the water than a pool in a warmer climate, where the water may be naturally closer to 80 degrees. The desired temperature rise (in degrees) per hour, to gauge heater efficiency, is also important for pool owners to understand. See the References for a chart on pool size and temperature rise and different strengths of pool heaters.

Bottom Line

To determine the best size of an electric heater for an in-ground pool, a pool owner needs to understand the total area of water that will be heated and determine the desired temperature and temperature rise for the pool water. Weighing the impact that the region and environment may play on unheated pool water may also play a part in selecting a heater with appropriate strength and efficiency options.

Source:

Poolgear.com: Pool Heaters Sizing

Inyopools.com: Pool Heater FAQ

Inyopools.com: Swimming Pool Calculations