Pool running costs: what a pool costs each month

The five lines

Pump electricity

kWh a month = watts × hours a day × 30 ÷ 1,000
cost = kWh × price per kWh

An example 1,500 W pump running 8 hours a day uses 360 kWh a month; at an example $0.17 per kWh that is $61.20. The DOE suggests starting at 6 hours of filtration a day and adding half an hour at a time only if the water isn’t clear. Dropping to 6 hours brings the same pump to $45.90. Both run times are worked on how much it costs to run a pool pump 8 hours a day and how much it costs to run a pool pump 12 hours a day.

Why slower is so much cheaper

Pump affinity laws, as Pentair sets them out: flow is proportional to speed, and power to speed cubed. ENERGY STAR puts it plainly — half speed uses one-eighth the energy. At half speed the example pump would draw about 188 W, run 16 hours to move the same water, and cost about $15.30 a month: a 75% saving. Real pumps land close to that. The pump the DOE’s Building America guide measured at four speeds shows it:

The DOE’s Florida example pool used 3,000 kWh a year for pumping; a smaller pump saved 40%, fewer hours 60%, and both together 75%. The DOE also says to choose the smallest pump that does the job. Check what flow your pool actually needs on what size pump for a 20,000 gallon pool; a variable-speed pump still has to meet the minimum flow of a heater, salt cell or cleaner.

Heating

Heating is the line that can dwarf the others. A 125,000 BTU/h heat pump at COP 5 uses 7.33 kWh an hour; at the example $0.17 per kWh and 8 hours a day that is about $299 a month — nearly five times the example pump line. The details, and what fewer hours do, are on what a heat pump pool heater costs per month. Gas and propane are compared in pool heater vs heat pump.

Two figures from the DOE do most of the work here: a cover cuts heating energy 50–70%, and each degree of extra pool temperature costs 10–30% more energy. Kept covered whenever nobody is swimming, the example heat pump’s $299 would drop by about $149 at the DOE’s low end.

Chemicals

Your own receipts are the only reliable figure, because chlorine demand depends on sun, swimmers, rain and debris. To estimate, work out how much chlorine your pool uses. If a 15,000-gallon pool loses an example 2 ppm of chlorine a day, it needs about 30.7 fl oz (3.8 cups) of 12.5% liquid chlorine a day — about 7.2 gallons a month. Multiply by what you pay per gallon, and add acid, stabilizer and anything else you buy.

The DOE says a cover cuts chemical consumption 35–60%. Testing before you dose, instead of adding a fixed amount on a schedule, keeps you from buying chlorine and acid the water didn’t need.

Top-up water

gallons per inch = surface (sq ft) × 0.623
top-up a month = gallons per inch × inches lost a week × 30 ÷ 7
cost = gallons ÷ 1,000 × price per 1,000 gal

A 16 × 32 ft pool has 512 sq ft of surface, so each inch of level is about 319 gallons. Losing an example 1 inch a week is about 1,368 gallons a month, about $6.84 at an example $5 per 1,000 gallons. Water is often the smallest line, unless a leak is hiding in it.

How much a pool loses depends on climate. The Southern Nevada Water Authority puts the average Las Vegas in-ground pool at 48.6 gallons per square foot a year — about 1.5 inches a week, or roughly 24,900 gallons a year for this pool. Cooler, more humid places lose less. SNWA says covers cut evaporation by 90%; EPA WaterSense says up to 95%; the DOE’s figure for total make-up water saved is 30–50%, because covers come off for swimming and splash-out continues. Round pools work the same way: how many gallons per inch in a 24 ft round pool.

The first fill is a one-off cost, and sewer charges can double it if your utility bills sewer on all water used. See how long it takes to fill a 10,000 gallon pool with a garden hose, how long and how much to fill a 20,000 gallon pool and how long it takes to fill a 24 ft round pool.

Salt cell

A salt chlorine generator draws power while it runs, usually alongside the pump. An example 150 W cell running the same 8 hours a day uses 36 kWh a month, about $6.12 at the example rate. Against that, the chlorine line mostly disappears — but salt pools usually buy more acid, the salt itself needs topping up as water is replaced, and the cell eventually needs replacing. See salt water pool basics.

An example month

The same example is worked line by line on how much it costs to run a pool per month; change any number in the pool running cost calculator to your own and the total follows.

Where the savings are

1. Pump hours and speed. Usually the biggest line without a heater. Start at 6 hours; consider variable speed if you run long hours.
2. A cover. DOE: 50–70% off heating, 30–50% less make-up water, 35–60% less chemical. It does nothing for the pump.
3. Temperature. Each degree costs 10–30% more heating energy; 80°F instead of 82°F is a real saving.
4. Time-of-use rates. If your utility charges less at certain hours, a timer can move pump and heater hours there.
5. Dose by test. It is the cheapest saving on the chemical line.