Calculator inputs
Example data table
| Pool area (sq ft) | Season (days) | Evap (in/day) | Cover reduction (%) | Energy type | Estimated season savings |
|---|---|---|---|---|---|
| 350 | 120 | 0.15 | 80 | Electric | $210–$380 |
| 450 | 150 | 0.20 | 85 | Gas | $320–$620 |
| 600 | 180 | 0.25 | 90 | Electric | $520–$980 |
Ranges reflect changing weather and user-entered chemical/cleaning assumptions.
Formula used
Water saved
- Uncovered gallons/day = Area × Evap(in/day) × 0.623
- Season water saved = Uncovered gallons/day × Days × Reduction%
- Water cost saved = Water saved × (Water price / 1,000)
Heating savings
- Latent heat ≈ 970 BTU per pound of water
- 1 gallon ≈ 8.34 pounds → ~8,080 BTU per gallon
- Replacement warming adds 8.34 × ΔT BTU per gallon
- Input energy = (BTU saved) ÷ Heater efficiency
- Electric: kWh = BTU ÷ 3,412; Gas: therms = BTU ÷ 100,000
Other savings
- Chemicals saved = Weekly chemical cost × Weeks × Reduction%
- Cleaning value saved = Weekly hours × $/hour × Weeks × Reduction%
- Total season savings = Water + Heating + Chemicals + Cleaning
How to use this calculator
- Enter pool surface area and your season length in days.
- Set uncovered evaporation and the cover reduction percent.
- Add local water price and your typical pool temperature target.
- Choose heater type, energy price, and efficiency for cost savings.
- Include weekly chemicals and cleaning effort for fuller totals.
- Press Calculate savings to view results above the form.
- Use the download buttons to export your latest calculation.
Evaporation is the largest hidden pool loss
Daily evaporation removes water and heat from an uncovered pool. A practical range is 0.10–0.30 inches per day, depending on wind, humidity, and water temperature. The calculator converts inches to gallons using 0.623 gallons per inch over one square foot. When a cover reduces evaporation by 50–90%, the saved gallons become your baseline for cost and energy savings.
Translating saved gallons into water cost
Water savings depend on your local rate per 1,000 gallons. If your pool saves 10,000 gallons over the season, a $6.50 rate yields $65 in overall refill savings before any heating benefits. In many areas, sewer or refill surcharges increase the effective rate. Enter the combined price you pay to avoid underestimating the value of reduced replacement water.
Heating impact and efficiency assumptions
Evaporation carries away latent heat, roughly 970 BTU per pound of water. With 8.34 pounds per gallon, that is about 8,080 BTU per gallon lost. The tool also accounts for warming replacement water using 8.34 × ΔT BTU per gallon. Saved BTU is converted to kWh (÷3,412) or therms (÷100,000), then adjusted by heater efficiency to estimate real utility cost savings.
Chemical and maintenance savings add up
Covers can reduce debris load and sunlight exposure, which may lower sanitizer demand and cleanup time. The calculator models this with weekly chemical spending and weekly cleaning hours, then applies your expected reduction percentages. Even modest changes matter: a $18 weekly chemical budget with a 35% reduction over 150 days saves about $135. Time savings are valued using your chosen hourly rate.
Reading payback and lifetime value
Season totals are annualized to compare against cover cost. Payback is estimated as cover cost divided by annualized savings, so a $240 cover and $240 annual savings implies about one year payback. Lifetime value multiplies annual savings by cover lifespan and subtracts the purchase cost. Use these outputs to compare cover types, update inputs for local weather, and plan replacements on schedule.
FAQs
What evaporation rate should I use?
Start with 0.15–0.20 in/day for mild conditions. Use 0.25–0.30 in/day for windy, hot, or very dry weeks. If you track water additions, adjust the rate until seasonal gallons align with real refills.
Should I include sewer charges in water price?
Yes, if your bill charges sewer on metered water and it applies to refills. If sewer is fixed, exclude it. The goal is a realistic price per 1,000 gallons that matches your local billing structure.
How do I estimate pool surface area?
For rectangles, multiply length by width. For circles, use π × radius². For freeform shapes, break the surface into simple sections and add them, or use an approximate average length and width.
Does heater efficiency change the results?
Yes. Lower efficiency means you must buy more input energy to replace the same lost heat. If you are unsure, use 80–95% for many heaters and adjust once you confirm your system’s performance.
Will a cover always reduce chemical use?
Often, but not always. Covers reduce debris and UV exposure, yet water balance still depends on bather load, rain, and filtration. Use conservative reductions first, then refine after a few weeks of real testing and logs.
Can I compare two cover types with this tool?
Yes. Run the calculator twice using different evaporation, chemical, and cleaning reduction percentages for each cover. Download CSV or PDF for each run to compare payback, annual savings, and net value side by side.