Pool Heating Calculators

Heating a pool is mostly four questions, and they share one underlying answer: how big is your pool. Surface area sets how much heat you lose to the air every hour; volumesets how much heat you have to put in to raise the temperature; and the gap between those two — the two-number method — is the basis of every honest BTU (British Thermal Unit) figure on this hub. Most clone calculators quote a “BTUs per gallon” rule and miss the surface entirely.

The sizingquestion opens the cluster. A pool heater is usually undersized because the buyer reads the rule and doesn't account for the surface bleeding heat to the wind beside the heater that's adding it. The honest answer is a BTU range, not a single fake-precise number — and the cover wedge is enormous: a cover saves about 54,600 BTU every hour the pool sits, which is the difference between needing a 250 k BTU heater and a 400 k.

Once sized, the next question is what the heater actually costs to run. The popular “$46 to heat the pool” figure is the one-time heat-up. The number your bill cares about is the monthly maintenance cost — often near $1,100, depending on fuel choice — and the cost calculator handles four fuel types evenly: gas, propane, heat pump, and electric resistance. It surfaces the per-degree slope (heating cost scales with the gap between target and air, not with absolute temperature) and the cover-payback headline: about $719 a month saved, a $200 cover paying back in roughly eight days.

The lossquestion is its own physics. Evaporation is vapour-pressure-driven and humidity-dependent — your weather matters more than your pool. The evaporation calculator gives you gallons per day and per week from your actual climate, with the cover wedge meeting the heating cover wedge here: a cover cuts evaporation about 90 %, which turns out to be most of a cover's heating benefit. The reduced surface conduction is the smaller piece.

The timequestion closes the cluster. “How long to heat to 86 °F by Saturday” is the planning answer no rule-of-thumb gives, and the honest climb is usually longer than expected — about 15 hours where the back-of-envelope predicted 10, because the pool sheds heat while it warms. Net power, not output, drives the climb.