Pool Heating Cost Calculator
BTU Needed Is Fixed; Cost Depends on Fuel
Raising a pool's temperature by a given number of degrees always requires the same amount of energy delivered to the water, regardless of what's generating it — but the dollar cost of that energy varies enormously depending on whether the heater burns natural gas, propane, or runs on electricity, and how efficiently it converts fuel into heat. This calculator separates those two steps: first the physics (BTU needed), then the economics (fuel units and dollar cost) for whichever fuel type actually powers the heater.
The Formula
Input Energy = BTU Needed / Efficiency
Cost = (Input Energy / Fuel BTU per Unit) × Cost per Unit
The 8.34 constant is the weight in pounds of a gallon of water, and one BTU is defined as the energy needed to raise one pound of water by one degree Fahrenheit — so gallons × 8.34 × degrees of rise gives the raw energy requirement directly. Dividing by efficiency accounts for energy lost as waste heat rather than transferred to the water.
Worked Example
| Step | Value |
|---|---|
| BTU needed | 2,335,200 BTU |
| Input energy required (82% efficiency) | 2,847,805 BTU |
| Time to heat | 15.6 hours |
| Natural gas needed (100,000 BTU/therm) | 28.48 therms |
| Cost at $1.20/therm | $34.17 |
The same BTU requirement translates to roughly 31.12 gallons of propane or about 834.6 kWh of electricity — the physics doesn't change, only the fuel-specific conversion and unit price do.
Where This Calculation Matters
- Choosing between gas and electric heat pumps — comparing projected operating cost, not just purchase price, over a season of use.
- Budgeting seasonal heating — estimating what it costs to bring a pool up to swimming temperature at the start of the season, or to maintain it through cooler stretches.
- Evaluating efficiency upgrades — a higher-efficiency heater lowers input energy required for the identical BTU delivered, directly cutting fuel cost.
How to Use This Calculator
- Enter your pool volume in gallons.
- Enter the current and target water temperature in °F.
- Enter your heater's rated output in BTU/hr.
- Enter the heater's efficiency as a percentage.
- Select the fuel type — natural gas, propane, or electric.
- Enter the cost per unit of that fuel (per therm, gallon, or kWh).
- Select Calculate to see estimated cost and heating time.
Related Calculations
Size the heater itself first with the Pool Heater Size Calculator, or check the Pool Volume Calculator if your gallon figure needs verifying.