Interactive planning tool

Pool Heater Size Calculator

Estimate a pool heater’s water-only BTU-per-hour output from pool gallons, desired temperature rise and target warm-up time.

Pool gallonsStarting water °FTarget water °FDesired heat-up hours

Water-only output floor125,000 BTU/hr

Add site-specific allowance for evaporation, wind, plumbing and equipment performance.

Method: water load = gallons × 8.34 × temperature rise. This planning result does not approve equipment, gas supply, electrical work, plumbing, roof loading or permits. Confirm the final system with current manufacturer data and qualified local professionals.

How to use this estimate

Enter the pool’s actual gallons when known; dimensions-based volume estimates can compound rounding errors. Choose a temperature rise that reflects the water at startup, not the afternoon air temperature, and use the longest warm-up window that still fits your routine. The result is a water-only planning floor. Wind, evaporation, cold air, plumbing losses and recovery after swimmer use can increase the output required, so compare the estimate with a qualified installer’s heat-loss calculation and the manufacturer’s rating conditions.

Read the complete sizing method