Pool Heating Cost Calculator
Estimates how much it costs to heat your pool to a desired temperature based on pool volume, temperature rise needed, heater type, and energy price. Perfect for budgeting before pool season or evaluating heater upgrades.
Last updated: September 2026
Formula below · 1 source (Wikipedia) · Updated Sep 2026
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About this calculator
Heating water requires a known amount of energy: one BTU raises one pound of water by 1°F. Since water weighs approximately 8.34 lbs per gallon, the total heat energy required is poolVolume × 8.34 × tempIncrease BTUs. The formula converts this to cost: heatingCost = (poolVolume × 8.34 × tempIncrease × energyCost) / (efficiency × 1000). Here, energyCost is in $/therm (1 therm = 100,000 BTU) and efficiency is entered as a percent, so efficiency × 1000 equals (efficiency / 100) × 100,000 BTU per therm. For an electric heater, convert your rate first: $/therm = $/kWh × 29.3, and enter a heat pump’s COP × 100 as the efficiency (for example 500 for COP 5). Higher heater efficiency means fewer energy units purchased per BTU delivered to the water. Heat pumps achieve efficiency ratings above 100% (COP 3–5) because they move heat rather than generate it.
How to use
Example: 20,000-gallon pool, needs a 10°F temperature rise, gas heater at 85% efficiency (enter 85), gas costs $1.20/therm. Step 1 — heat energy in BTUs: 20,000 × 8.34 × 10 = 1,668,000 BTU. Step 2 — apply formula: (20,000 × 8.34 × 10 × 1.20) / (85 × 1000) = 2,001,600 / 85,000 ≈ $23.55. Note this is the one-time cost to raise temperature; maintaining temperature daily adds the cost of replacing heat lost overnight and to evaporation.
Frequently asked questions
How much does it cost to heat a pool with a gas heater versus a heat pump?
Gas heaters typically cost more to operate per BTU delivered because natural gas, while relatively cheap per therm, is burned at fixed efficiencies of 80–95%. Heat pumps extract heat from ambient air and can deliver 3–5 units of heat for every unit of electricity consumed, giving them effective efficiencies of 300–500%. For example, heating a 20,000-gallon pool by 10°F might cost $20–30 with a heat pump versus $80–120 with a gas heater depending on local energy prices. However, heat pumps heat water more slowly and perform poorly below 50°F air temperature.
Why does pool volume in gallons matter for calculating heating costs?
Because water has a fixed heat capacity — it takes exactly 1 BTU to raise 1 lb of water by 1°F — the total energy needed scales directly with the mass of water in the pool. Since water weighs 8.34 lbs per gallon, a larger pool requires proportionally more energy to heat by the same number of degrees. Underestimating pool volume leads to underestimating heating costs and potentially undersizing your heater. You can find your pool's volume using a separate pool volume calculator if you don't already know it.
How can I reduce pool heating costs without sacrificing comfort?
Using a solar pool cover (blanket) when the pool is not in use is the single most effective measure — it can reduce heat loss by up to 70% overnight. Lowering your target temperature by just 2°F can noticeably reduce ongoing heating costs. Installing a solar thermal heating system to supplement a gas or electric heater offsets fuel costs substantially. Finally, heating the pool only when it will be used rather than maintaining a constant temperature around the clock can cut seasonal costs in half.