Pool Heater Size Calculator
The heater figure is the heat required to raise the water you have, spread over the hours you allow. Wind and surface loss are not included.
Result: heater
Enter a volume greater than 0.
How Many BTU per Hour Do You Need?
BTU = gallons × 8.34 × temperature rise in F
BTU per hour = BTU ÷ hours
Sample, not a recommended rise: 15,000 gallons, up 10 F, over 24 hours, is 52,125 BTU/h. The heat total before dividing by hours is 1,251,000 BTU.
A surface-loss or wind factor is not verified, so it is not subtracted and not added. The number is only the water's own heat.
Heater Results for One Sample Pool
15,000 gallons and a 10 F rise, at three different hour entries. The rise is a sample, not advice about how warm the pool should be.
| Hours you allow | BTU per hour |
|---|---|
| 12 | 104,250 BTU/h |
| 24 | 52,125 BTU/h |
| 48 | 26,063 BTU/h |
Common Mistakes With the Pool Heater Size Calculator
- Quoting the BTU total as if it were already per hour. Divide by the hours you allow.
- Adding a wind penalty from memory. That factor is not verified.
- Skipping gallons. The volume calculator is the place to get them.
Get the Gallons First
Pool Heater Size Calculator FAQ
How many BTU does it take to raise 15,000 gallons by 10 F?
1,251,000 BTU, before you divide by the hours you allow. This ignores surface loss.
Does this page subtract wind or surface heat loss?
No. A surface-loss factor is not verified.
What is the heater formula?
Gallons times 8.34 times the temperature rise in Fahrenheit, then divide by hours to get BTU per hour.