Choosing the correct pool heater depends on pool size, desired heat-up time, climate, and heater type. Undersized heaters struggle to maintain temperature; oversized heaters heat faster with less runtime.
Heater Types Explained
Gas Pool Heaters (Natural Gas or Propane)
- Fastest heat-up
- Works in any climate
- Higher operating cost
Best for: Quick heating, spas, occasional use
Electric Heat Pumps
- Most energy-efficient
- Slower heat-up
- Performance depends on air temperature
Best for: Warm/moderate climates, consistent heating
Solar Pool Heaters
- Lowest operating cost
- Weather dependent
- Slowest heat-up
Best for: Supplemental heating, sunny regions
BTU Requirements for Natural Gas and Propane
Based on Dimensions and Surface Area (sq. ft.)
| Pool Dimensions | Surface Area | Minimum BTU |
|---|---|---|
| 14′ x 28′ | 392 | 130,700 |
| 15′ x 30′ | 450 | 150,000 |
| 16′ x 32′ | 512 | 170,700 |
| 18′ x 36′ | 648 | 216,000 |
| 20′ x 40′ | 800 | 266,700 |
| 24′ x 44′ | 1,056 | 352,000 |
BTU Requirements for Heat Pumps
Based on Gallons
| Pool Size (Gallons) | Minimum BTU |
|---|---|
| Up to 15,000 | 90,000 |
| 15,000 – 25,000 | 110,000 |
| 25,000 – 35,000 | 130,000 |
| 35,000 – 50,000 | 150,000+ |
Hourly Temperature Increase
Based on Surface Area (sq. ft.) and BTU
| Surface Area | 250K BTU | 350K BTU | 400K BTU |
|---|---|---|---|
| 300 | 2.0º | 3.0º | 3.5º |
| 400 | 1.75º | 2.5º | 2.75º |
| 500 | 1.5º | 2.0º | 2.5º |
| 600 | 1.25º | 1.5º | 2.0º |
| 700 | 1.0º | 1.25º | 1.5º |
| 800 | 0.75º | 1.0º | 1.25º |
| 1,000 | 0.5º | 0.75º | 1.0º |
Gas Supply & Electrical Requirements (Very Important)
Gas Heaters
- Must verify gas line size and meter capacity
- Undersized gas supply = poor performance or ignition issues
Heat Pumps
- Require dedicated breaker
- Higher amperage draw
- Longer electrical run considerations
⚠️ Heater sizing is meaningless if utilities are undersized.
Factors That Increase Heater Size Needs
You may need a larger heater if your pool has:
- Attached spa
- Waterfalls or spillovers
- High wind exposure
- Night swimming
- Minimal sun exposure
- Short heating windows (weekends only)
Common Heater Sizing Mistakes
❌ Choosing smallest BTU to save money
❌ Ignoring climate and wind
❌ Forgetting spa heating needs
❌ Not checking gas or electrical supply
✅ Size for how fast you want heat, not just pool volume
Replacing an Existing Heater?
Check the heater data plate for:
- BTU input
- Gas type (NG / LP)
- Voltage & phase
- Min/max flow rate
If upgrading, going one size larger almost always improves satisfaction.
If you’re unsure, contact us and we’ll help you choose the correct heater.
