Sample inputs and estimated outputs
| Scenario | Annual cost | Energy use | Annual savings | Payback |
|---|---|---|---|---|
|
Current (Gas)
Area 450 ft², setpoint 84°F, air 72°F, 180 days, loss 10
|
$5,545.58 | 2,981 therms | — | — |
|
Improved (Heat pump + cover)
Loss 6, COP 5, runtime 0.90, rebate 400
|
$1,586.78 | 8,038 kWh | $3,958.79 | 0.71 yrs |
How the estimate is calculated
- Temperature difference: ΔT = max(Setpoint − AirTemp, 0)
- Heat loss rate: BTU/hr = LossCoeff × SurfaceArea × ΔT
- Annual heating load: AnnualBTU = BTU/hr × 24 × SeasonDays × RuntimeFactor
- Optional warm-up: StartupBTU = Gallons × 8.34 × ΔF × weekly starts (annualized)
- Fuel conversion: Gas therms = BTU / 100,000 / efficiency
- Electric conversion: kWh = BTU / 3,412 / efficiency, or / COP for heat pumps
- Annual cost: EnergyCost + Maintenance
- Savings: CurrentAnnualCost − ImprovedAnnualCost
- Payback: (UpgradeCost − Rebate) ÷ AnnualSavings
- NPV: Sum of discounted savings over years − NetUpfront
Steps to get a realistic savings estimate
- Enter pool surface area, setpoint, average air temperature, and heated season days.
- Set the current heat-loss coefficient to match uncovered or covered conditions.
- Choose your current heater type and enter efficiency (or COP for heat pumps).
- Choose the improved heater type, and reduce the improved heat-loss coefficient if adding a cover.
- Enter local energy prices, expected maintenance, and the upgrade cost and rebate.
- Press Calculate Savings to see costs, savings, payback, and NPV.
- Use Download CSV or Download PDF after calculating.
Season length and temperature targets shape costs
Heating demand grows with the temperature gap between water and air, multiplied across the heated season. A 10°F higher setpoint can materially increase annual load, because ΔT applies every hour. For example, a 450 ft² surface, 12°F ΔT, and 180 days implies a larger annual BTU requirement than the same pool heated only 90 days. Shortening the season often delivers the fastest savings overall.
Heat-loss coefficient captures cover and wind effects
The heat-loss coefficient (BTU/hr·ft²·°F) is the calculator’s control for evaporation, convection, and wind. Uncovered pools commonly fall near 8–12, while effective covers and windbreaks can push the value lower. Dropping the coefficient from 10 to 6 reduces the hourly loss by 40% at the same ΔT. Combining a lower coefficient with a better runtime factor reflects both physical loss reduction and smarter operating schedules.
Efficiency and COP drive energy price exposure
Heater performance converts thermal load into purchased energy. Gas heaters use efficiency, while heat pumps use COP, which varies with air temperature. With the same annual BTU load, a COP 5 heat pump needs about one-fifth the electric input of resistance heating. Energy prices then matter: if electricity is $0.18/kWh and gas is $1.80/therm, the cheaper option depends on equipment performance, climate, and how long you maintain setpoint.
Payback and NPV translate savings into decisions
Upfront cost matters, but timing matters too. Simple payback divides net upfront cost by annual savings, giving an easy comparison across upgrades. Net present value discounts future savings, so higher discount rates favor quicker returns. If annual savings are stable, NPV becomes a single decision score: positive NPV suggests the upgrade beats your chosen hurdle rate over the selected analysis years.
Practical calibration improves reliability
To improve accuracy, calibrate inputs to your recent bills. Start with realistic energy prices and efficiency or COP, then adjust the current heat-loss coefficient until the model matches your typical seasonal spend. After that, test improvements one at a time: cover, setpoint change, runtime reduction, or heater replacement. Sensitivity checks—like ±10% on ΔT or coefficient—show how robust your savings estimate is.
FAQs
What heat-loss coefficient should I start with?
Use 8–12 for uncovered pools and 4–8 with a good cover. Start near 10 if you lose heat quickly at night, then calibrate until the “current annual cost” resembles your recent seasonal spending.
When should I enter COP instead of efficiency?
Enter COP only when heater type is “Heat pump.” COP reflects heat delivered per unit of electricity and typically ranges from 3 to 7, depending on air temperature and unit design.
Why does the calculator show negative savings?
Negative savings means the improved scenario costs more than your current setup. This can happen with higher energy prices, low COP during cold weather, or if the “improved” heat-loss settings are not actually lower.
How do I model adding a solar cover without changing heaters?
Keep the heater type the same and reduce the improved heat-loss coefficient and runtime factor. Covers mainly reduce evaporation losses, so the coefficient change usually drives most of the savings.
Does this include circulation pump electricity?
No. This tool focuses on heating energy. If you want a broader operating-cost view, add pump kWh separately and compare timer schedules, variable-speed pumps, and filtration needs.
How can I validate the estimate quickly?
Match the current annual cost to your historical bills by adjusting the current coefficient and runtime factor. Then change only one variable at a time—cover, setpoint, season days, or heater type—to see realistic deltas.