This article is provided courtesy of PoolGear Plus.
The chart below is an easy way to size a swimming pool heater. Simply determine the surface area square footage and the desired temperature. Then refer to the chart for the amount of BTUs required to heat up your swimming pool.
For example: A 400 sf pool with a temperature of 20 degrees. The heater output per hour needs to be at least 223,700 BTUs to heat your swimming pool in 24-hours.
Pool Heater Sizing Chart: 24-hour Period
| Pool Size (sf) | 10 Degrees | 15 Degrees | 20 Degrees | 25 Degrees | 30 Degrees |
| 200 | 55,900 | 83,800 | 111,840 | 139,800 | 167,760 |
| 300 | 83,880 | 125,820 | 127,700 | 209,700 | 251,640 |
| 400 | 111,650 | 167,775 | 223,700 | 279,625 | 335,550 |
| 500 | 139,810 | 209,715 | 279,620 | 349,525 | 419,430 |
| 600 | 167,770 | 251,655 | 335,540 | 419,435 | 503,310 |
| 700 | 195,720 | 293,595 | 391,460 | 489,325 | 587,190 |
| 800 | 223,690 | 335,535 | 447,380 | 559,225 | 671,070 |
| 900 | 251,650 | 377,475 | 503,300 | 629,125 | 754,950 |
| 1,000 | 279,610 | 419,415 | 559,220 | 699,025 | 838,830 |
To calculate the heat up time, use this formula: Pool Gallons X 8.33 (the weight of 1 gallon of water) X Temperature Rise = Output BTUs needed to acheive desired water temperature in 48-hours.
Pool Maintenance Heater Sizing Chart: Outdoors, 3.5 mph wind
Use this chart to maintain heat in normal conditions.
| Pool Size (sf) | 10 Degrees | 15 Degrees | 20 Degrees | 25 Degrees | 30 Degrees |
| 200 | 21,000 | 31,500 | 42,000 | 52,500 | 63,000 |
| 300 | 31,500 | 47,300 | 73,000 | 78,800 | 94,500 |
| 400 | 42,000 | 63,000 | 84,000 | 105,000 | 126,000 |
| 500 | 52,500 | 78,800 | 105,000 | 131,000 | 157,000 |
| 600 | 63,000 | 94,500 | 126,000 | 157,000 | 189,000 |
| 700 | 73,400 | 110,000 | 147,000 | 184,000 | 220,000 |
| 800 | 84,000 | 126,000 | 168,000 | 210,000 | 252,000 |
| 900 | 94,500 | 142,000 | 189,000 | 236,000 | 284,000 |
| 1,000 | 105,000 | 157,000 | 210,000 | 263,000 | 315,000 |
These charts must be consulted when you're perforiming a swimming pool heaters comparison. This way you can have an estimate of how much energy is required to heat your pool.
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