Heating water takes a known amount of energy. The BTUs to raise the pool a few degrees — gallons × 8.34 × Δtemperature — convert to fuel cost and heater runtime.
The example
20,000 gal, raise 10°F.
| A | B | |
|---|---|---|
| 1 | Item | Value |
| 2 | 20000×8.34×10 | — |
| 3 | BTUs | → ~1,668,000 |
The formula
The formula:
How it works
How it works:
- Pounds of water = gallons × 8.34; × the degree rise = BTUs (1 BTU raises 1 lb 1°F).
- Divide BTUs by the heater output (BTU/hr) for heating hours (allow for efficiency/losses).
- For cost: BTUs ÷ fuel energy × price (e.g. ÷ 100,000 for therms of gas).
- A cover cuts evaporation losses dramatically — the cheapest heat is heat you don’t lose.
Educational use only — not chemical-safety or professional advice. Pool chemical dosing varies by product strength, water chemistry, and local rules. Always follow the product label, add chemicals to water (never water to chemical), test before and after, and never mix chemicals. Verify with a professional.
Try it: interactive demo
Gallons, temp rise, heater BTU/hr.
Variations
Heating hours
BTU ÷ heater output:
Gas cost (therms)
BTU ÷ 100,000 × price:
With efficiency
Real fuel BTUs:
Pitfalls & errors
8.34 lb/gal. Water weighs 8.34 pounds per gallon.
Efficiency. Heaters aren’t 100% — divide by efficiency for fuel.
Cover saves heat. Evaporation is the biggest loss — this ignores losses.
Practice workbook
Frequently asked questions
How do I calculate pool heating energy in Excel?
How long will the heater take?
How do I get the gas cost?
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