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Calculate pool heater size in BTU, heating time, and operating costs. Compare gas, propane, electric, heat pump, and solar heater options for your pool.
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Pool heaters are sized based on the BTU (British Thermal Units) needed to raise the water temperature to your desired level:
8.33 = lbs per gallon of water
25% safety factor for heat loss
Pool: 20,000 gallons
Current: 68°F
Desired: 82°F
Rise: 14°F
BTU = 20,000 × 8.33 × 14 = 2,332,400 BTU
Recommended = 2,332,400 × 1.25 = 2,915,500 BTU
Round to standard: 300K BTU heater
At 82% efficiency:
Time = 2,332,400 / (300,000 × 0.82) = 9.5 hours
| Type | Efficiency | Initial Cost | Operating Cost | Best For |
|---|---|---|---|---|
| Natural Gas | 82% | $1,500-3,500 | Medium | Fast heating, any weather |
| Propane | 82% | $1,500-3,500 | High | No gas line available |
| Electric | 100% | $500-1,500 | Very High | Small pools, spas |
| Heat Pump | 500%+ COP | $2,500-5,000 | Low | Warm climates, long seasons |
| Solar | 80% | $3,000-8,000 | Free | Sunny climates, eco-friendly |
Reduces heat loss by 50-70%, saves $300-800/year
Fence or landscaping reduces wind evaporation by 25-50%
Each 1°F reduction saves 10-30% on heating costs
5× more efficient than gas, 80% cost savings
Size depends on pool volume, desired temperature rise, and climate. A 20,000-gallon pool typically needs 250K-400K BTU. Gas heaters heat faster but cost more to operate. Heat pumps are cheaper to run but heat slower (1-3 degrees/hour vs 5-10 degrees/hour for gas).
Gas heaters: 8-12 hours for a 10-15°F rise. Heat pumps: 24-72 hours for the same rise. Solar heaters: 3-7 days depending on sun exposure. Using a pool cover reduces heating time by 30-50%.
In warm climates (>50°F), yes. Heat pumps cost $2,500-5,000 vs $1,500-3,500 for gas, but operating costs are 80% less. Payback period is 2-4 years in areas with long swim seasons. Not recommended for cold climates or quick heating needs.
Use a pool cover instead. Running a heater overnight without a cover wastes 50-70% of heat to evaporation. A solar cover retains heat and costs $50-200 vs $10-40/night for gas heating. Only heat during day when needed.
Recreational swimming: 78-82°F. Lap swimming: 76-78°F. Young children: 82-84°F. Therapy pools: 86-88°F. Every 1°F above 78°F adds 10-30% to heating costs. Most find 80°F comfortable for general use.
Yes, for large pools (40,000+ gallons) or faster heating. Install two smaller heaters rather than one oversized unit for redundancy and efficiency. Also common to use solar as primary with gas backup for cloudy days or rapid heating.