Recommended H-Series Heaters for Swimming Pools. 

Determine the pool surface area by multiplying the length of the pool in feet by the width. Use the chart above to determine the heater size for your pool. 

A note about heater size: A pool heater should heat the pool, on average, one degree an hour. Once the heater is sized to the pool, stepping up one or two sizes will decrease the time to heat. 

CAUTION: If you are replacing an existing heater, the new heater size is limited by the diameter of the existing gas supply pipe. Gas pipe is sized according to BTU’s required. Installing a larger heater than the existing pipe can supply will result in a sporadic or non-operating heater.