Pool Heater Sizing Calculator
An undersized heater takes too long to reach temperature and may never overcome heat loss in cooler weather. This calculator determines the minimum BTU output needed based on pool volume, desired temperature rise, and target heat-up time.
Pool Heating Parameters
Heat loss varies with wind exposure, humidity, ambient temperature, and pool surface area. A pool cover reduces heat loss by 50–70%. Actual heating performance depends on heater efficiency rating and environmental conditions.
Pool Heating Formula
The fundamental heat energy formula:
BTU Required = Pool Volume (gal) × 8.34 × Temperature Rise (°F)
Where 8.34 is the weight of one gallon of water in pounds. To convert to BTU/hr output needed, divide by the desired heat-up time in hours and account for heat loss.
Heater Types Comparison
| Type | Efficiency | Operating Cost | Best Climate |
|---|---|---|---|
| Gas (standard) | 80–84% | $300–600/mo | Any (fast heating) |
| Gas (high-eff) | 90–95% | $250–500/mo | Any |
| Heat Pump | COP 5–7 | $100–200/mo | Above 50°F ambient |
| Solar Panels | N/A | $0 operating | Sunny climates |
Frequently Asked Questions
How many BTU do I need for a 15,000 gallon pool?
To raise a 15,000 gallon pool by 15°F in 24 hours: 15,000 × 8.34 × 15 = 1,876,500 BTU total, or about 78,200 BTU/hr before heat loss. With heat loss (no cover), a 100,000–150,000 BTU gas heater is typical. With a cover, a 100,000 BTU unit is sufficient.
Heat pump vs. gas heater?
Heat pumps cost 3–5 times more upfront ($3,000–6,000 vs. $1,500–3,000 for gas) but operate at 1/3 to 1/5 the monthly cost. In warm climates (Florida, Arizona, Texas), heat pumps pay back in 2–3 years. In cold climates, gas heaters are more practical because heat pumps lose efficiency below 50°F ambient.