Pool Heating Cost Calculator

Your biggest expense is that first warm-up. Once the water is warm, holding it there comes down to wind, shade, and whether the pool gets covered.

A BTU is just a measure of heat. It takes 8.34 BTU to lift one gallon of water by 1 degree F, which is why a large pool or a big temperature jump drives up the price. Start with your gallons, since every other number flows from them.

Not sure how many gallons you have? These common pool sizes suppose the water averages 4.5 ft deep:

A heat pump runs on electricity and pulls heat into the water. For every unit of power it draws, it delivers 5 units of heat, and that's why it usually costs less to run than a fuel-burning heater. A gas heater sends 82% of the gas it burns into the water as heat, and the rest goes to waste.

Electricity is priced at 18.16 cents per kWh, the US average reported by the EIA. Gas prices come from the EIA gas price table. Your rates might not match these, so check your bill for what you pay per unit of power or gas.

A few small habits bring the bill down, and there's a reason each one works:

• Put a cover on the pool each night, so the heat you already paid for doesn't escape.
• Only heat during the weeks you'll actually swim, so you don't warm water that sits untouched.
• Drop the temperature setting by a few degrees. Every extra degree costs more to reach, so trimming a little saves you money.

Heating and pumping are two different costs. A standard single-speed pump pulls roughly 1,725 watts, so running it 8 hours burns through about 13.8 kWh each day. To get the daily cost, multiply those kWh by 18.16 cents for each kWh.

When it's hot out or the pool got heavy use, add 1 to 2 hours of running time, which nudges that figure up slightly.