calcs.homes
calcs.homes
Enter your pool's surface dimensions, desired water temperature, and average air temperature to find the BTU output you need from a heater.
Estimate only — an uncovered pool in wind loses heat faster; a pool cover reduces the BTU needed.
We multiply pool surface area by the temperature rise needed — desired water temperature minus average air temperature — by a constant of 12 BTU per square foot per degree, a standard rule-of-thumb for heat loss from an uncovered outdoor pool. That raw figure is then rounded up to the next commonly sold gas heater size: 100k, 150k, 200k, 250k, 300k, or 400k BTU/hr.
The 12 BTU/sq ft/°F constant approximates the combined evaporative, convective, and radiant heat loss a typical outdoor pool experiences, which is why it's a common industry starting point even though it doesn't account for wind or humidity directly. Rounding up to a stock heater size matters because manufacturers only build a handful of BTU tiers — an undersized heater will struggle to reach or hold your target temperature.
It depends on your pool's surface area and how much you need to raise the temperature above average air temperature — enter your numbers above for a specific BTU recommendation.
Yes significantly — a cover cuts evaporative heat loss, often the biggest factor in pool heat loss, so a covered pool can often use a smaller heater or heat faster with the same size.