Help me with kWh math and other Pump Questions


Well-known member
Jul 18, 2013
Brownsburg, IN
Trying to do some research and some math but I’m getting confused and have some questions.

PB wants to put in a 1HP single speed pump. We will have 20k gal of water, a SWCG, a pool heater and 2” plumbing. (details in siggy line). Should I swap for a 1 HP 2 speed or 2 HP 2 speed pump? I’ve only ever had a single speed pump on previous pools.

So I assume that with a two speed pump to save money you would run the pump for example 12 hrs on low through the night and 12 hrs on high during the day (just an example as I know depending on temp, time of year, pollens, storms, bather load etc it changes). I would need to install a timer or something to switch between speeds?
What would automate speed change that is not a digital gadget? (Because cost, so many expenses when building a house)

Our PB recommends running the pool pump for 24 hrs a day because we have such hard limestone mineral rich water here in central Indiana that builds up and scales. Is this bologna? Wouldn’t proper pool chemistry combat this line of thinking?

Last but not least, math.

The 1HP pump is 8/16 amps and 230/115v
8x230=1840/1000=1.84 kWh

The 2 HP 2 speed is 10 amps and 230v. (Jandy Flo Pro 2hp 2 speed FHPM 2.0-2)
10x230=2300/1000=2.3 kWh

Average cost of electricity in Indiana as of Dec 2017 is 11.29 kWh.

Now how much would it cost to run the pump 24 hrs on low and 24 hrs on high for each pump?

Thank you for any help and any information!


TFP Expert
LifeTime Supporter
Jan 4, 2016
Sydney, NSW, Australia
Following Trouble Free Pool Care (TFPC) you'll probably run the PHPF 1.0 HP pump about 8 hrs per day in summer, 4 hrs when open but not swimming, none when closed, just to offer a very rough idea and for calculations.

You're unlikely to need to run low speed of a 2-speed version of that same pump for very many more hours, but possibly some more if skimming takes longer. Run times for either pump will be when you want the pool looking it's best, so debris is skimmed off the surface. Running overnight is sometimes done if power is a lot cheaper at night, and skimming cleanliness can be fit in.

On peak days of summer, the Aquapure Ei will need around 13 hours to generate enough chlorine. More on that below.

The pump will draw less power than it's full rating, but that's hard to predict, so I'll just do the math at the full rating. At 1,840 watts (1.84 kW), and $0.1129 per kWh, it costs 1.84 X $0.1129 per hour, or around $0.21 per hour or $5 per 24 hrs (or $1.66 for the more realistic 8 hrs).

No need to go up to 2 HP, so I'll just compare the same pump, as a 2-speed, model 'PHPF 1.0-2'. Usually low speed will draw around 1/4 the power, so I'll use 460 watts, $0.05 per hour, and $1.25 per 24 hours (or a more realistic 10 hours per day would be $0.50 per day).

Maybe you'd like a quick skim as part of that, say 2 hours at full speed, and 8 hrs at low speed:

2 hrs x 1.84 kW + 8 hrs x 0.46 kW = 7.36 kWh. And $0.1129 per kWh x 7.36 kWh = $0.83 per day

Chances are that you'll end up a bit lower than that on all options. Pump run time at 5 or 6 hours is enough for many situations.

It's also fair to mention that low speed is quieter than full speed, and that makes a difference for lots of people.

The Ei chlorinator sold in the US, to the best of my knowledge, is a 0.9 lb/day SWCG. If it's more than that, you can ignore the rest, but I need to mention it because a 0.9 lb/day SWCG is a bit small for a 20K gal pool, and will need 13 hours to make 3 ppm of FC, a typical amount needed in summer with lots of swimming. Something around 1.4 to 2.0 lbs per day would give you more flexibility. If the PB is expecting you to run 24 hrs per day of course this isn't a problem at all, except for your power bill, which the PB doesn't pay! If you're stuck with that chlorinator, then definitely get the 2-speed pump. And yes, your instincts are right, your water chemistry can be balanced with a minimum of pump time to keep it all stirred up, maybe an hour or so per day.