Pool Heating Calculator for Winter Months
This calculator helps determine the BTU (British Thermal Unit) rating needed for your pool heater. A BTU is the amount of heat required to raise the temperature of one pound of water by one degree Fahrenheit. Pool heaters are rated in BTU per hour (BTU/hr), indicating how much heat they can add to the pool each hour.
How Calculations Work:
- Initial Heat-Up BTU/hr: Total BTUs needed = Gallons × 8.34 (weight of water per gallon) × (Desired Temp – Ambient Temp). Divide by heat-up hours for hourly rate. This sizes the heater for bringing the pool up to temperature.
- Maintenance BTU/hr: Surface Area × (Desired Temp – Ambient Temp) × 12. This compensates for heat loss to maintain temperature in winter conditions (assumes moderate wind; actual loss may vary with covers, humidity, etc.).
- Choose the higher of the two for your heater size. For colder winters or faster heating, increase by 1.5× or 2×.
Cost Estimation:
- Costs are estimated per hour, day, and month of operation using the recommended BTU/hr, based on October 2025 US averages: Natural Gas $2.53/therm, Propane $2.52/gallon (91,500 BTU/gallon), Electric $0.165/kWh. Assumes 82% efficiency for gas/propane and COP=5 for electric heat pumps. Adjust for local rates and actual efficiency.
Sources: U.S. Department of Energy guidelines and standard pool heating formulas.