About this tool
The Pool Heating Time & Cost Calculator estimates how long and how much it costs to warm your pool by a chosen number of degrees, for both gas heaters and electric heat pumps. It starts from the fundamental heat requirement Q = gallons × 8.34 × ΔT°F, since one BTU raises one pound of water by one degree Fahrenheit. Everything runs locally in your browser and nothing is uploaded.
For a gas heater, run time = Q ÷ (rating BTU/hr × efficiency), the gas burned is Q ÷ 100,000 ÷ efficiency therms, and cost = therms × your price per therm. For a heat pump, the thermal energy is Q ÷ 3,412 kWh, run time = Q ÷ (rating BTU/hr), the electricity actually drawn is thermal kWh ÷ COP (a coefficient of performance of 5 means 5 units of heat per unit of electricity), and cost = electrical kWh × your price per kWh. Enter volume and temperatures in US units (gallons, °F) or metric (litres, °C) — the tool converts internally so the physics is identical.
Because the model computes ideal delivered heat, it does not include ongoing heat loss to air, evaporation, and the ground, which can be substantial for an uncovered pool. Real-world times run longer, especially overnight; a solar cover cuts overnight heat loss by roughly 50–70% and is the single biggest efficiency win. Use this as a strong planning estimate for how big a heater you need and what a warm-up will cost.