Proper heater size is based on the time required to heat pool or spa to the desired temperature.

If water is heated for each intended use and rapid heating is desired, a larger unit is required.

If water is gradually heated to the desired temperature and then maintained at that temperature, a smaller heater may be acceptable.

First determine desired temperature rise per hour using the chart below: Temperature rise per hour formula:

Gas Pool Heater sizes are determined by their BTU* output. Use the chart below to determine BTU required to raise the water temperature depending on the pool size.

POOL SIZE - SQUARE FEET

Gas pool heaters, gas pool heating,