How much does it cost to run a pool pump?

Old 07-10-03, 08:26 AM
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Question How much does it cost to run a pool pump?

Hello all.

We just had a new inground pool installed. The pool company takes the conservative approach and says run the pump 24/7. In discussing the issue with other pool owners on a pool forum similar to this board, there is no real consensus amongst owners/installers.

I know there is the issue of on/off cycles vs. continuous run times and the related wear issues, but for sake of discussion, I'm trying to simply determine the cost to run the pump.

The name plate ratings are:

1 HP pump with a service factor of 1.25 (I think this means the pump is effectively producing 1.25 hp. Is this correct?)

230 v/7.1 amps

Now here is where I get confused. One HP is 746 watts. Applying the service factor, I get 746*1.25=932.5 watts.

If I multiply the nameplate ratings, I get 230*7.1=1633 watts, a far cry higher that the earlier answer. (Also, I know I'm running at 240 volts, not 230, but presumably the current is correspondingly less than 7.1 to still equal 1633 watts. Correct?)

My cost per KWH of electricity is about 0.085. So for a 24 hour period, I should be paying:

WATTS/1000 * 0.085 * 24= Cost

If I use these two numbers, I get either $1.90 or $3.33 per day or a ~$43 difference per month.

I have no problem running the pump as necessary to do the job; just don't want to throw money down the drain .

Thanks in advance.

Old 07-10-03, 08:41 AM
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I'll leave the math to the pro electricians. Running a residential pool pump 24/7, in my never-to-be-humble opinion, is excessive. I run ours about 8 hours a day and that is more than sufficient. I did convert from cartridge filter to DE a couple of years ago which is a much more efficient filtering system, thereby allowing me to run the pump less unless I'm needing the extra run time for the solar heat (not needed during the summer, of course).
Old 07-10-03, 10:07 AM
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I too have a DE filter, and thus feel a reduced run time is appropriate. The pool company recommends 24/7, but IMHO they view it NOT in terms of what it will cost me, but from a standpoint of more water movement/filtration means less potential pool chemistry problems and completely avoids the issue of diminishing returns.

At the risk of answering my own post, after further reflection, I believe the HP rating represents OUTPUT and the Volt/Ampere nameplate data represents (more closely) the power input.

Further, the 230*7.1 is VOLT-AMPERES, not watts (and we are all billed for watts). So I need to research the "power factor" of the motor.

Help me out here guys. What's a good "assumption" here? 0.8?

If I use 0.9, then my cost to run the pump for 24 hours is (correct me if I'm wrong guys):

Volts*Amps*(Power Factor)/1000 * $$/KWH * 24 hr/day= X $/day

or in my case:

230*7.1*.9/1000 * 0.085 * 24 = $3.00 per day

This is much higher that the pool guys estimate of "Oh about a dollar a day."

I think I'll play with the run times on the pump.

Still open for comments and input however!

Old 07-10-03, 10:58 AM
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Here is kink to your calculations. Your pump doesn't run at the full 1HP 7.1amps. That is the full load rating. You need to put an ampmeter on it to determine what the normal use current draw is for a proper calculation.
Old 07-10-03, 11:09 AM
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Your calculations are wayyyy closer than the Pool Guy's.
Old 07-10-03, 11:56 AM
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Originally posted by joed
You need to put an ampmeter on it to determine what the normal use current draw is for a proper calculation.
I assume you are referring to the type that reads current by placing the loop of the ammeter around the supply wire.

Not a tool I'll probably easily find at the Home Depot rental counter, eh? And not one that I (as a layman) could justify buying just to satisfy a curiosity.

But I am curious and may have to scrounge around to find one.

Old 07-10-03, 05:55 PM
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Even if you read the amps with an ammeter you won't know the power factor, so you won't be a lot better off. The Service Factor refers to the overload the motor is capable of under certain conditions. Google for it if you want more info. You won't be too far off the mark if you assume about one kw per hp. I run my pump about 8 hours per day. Pretty good rate you got there, where are you?
Old 07-10-03, 06:02 PM
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Clamp on meter is one type. A standard multimeter could also be used but you would need to disconnect one lead and put the meter in series with the motor.
Old 07-10-03, 06:23 PM
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You are looking at approx $2-$3 per day for the pump running 24/7.
An example of a clamp-on amprobe
Greenlee AC Clamp On Meter
Item #: 158122
Model: CM-310
Old 07-10-03, 09:58 PM
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I think a clamp on ampmeter is a great investment for the avg guy. Its not that pricey it can eleminate a lot of guessing.
Old 07-11-03, 08:16 PM
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Either way you need to run the pump.

Ran mine 8 hrs daily, 4 morning 4 afternoon
not enough, used more chemicals(shock)

Now runs 4 morn 6 afternoon , pool looks great

all depends on weather, climate and use, you can always turn it on for a couple extra hours after a heavy use
What you save on elec. you will spend on chemicals

not rocket science, just try different ways till you find what works best for you. keep close eye on balance.

hard to clean dirty pool- easy to keep a clean pool clean

about $100 per month more on electric bill with pool ??
Old 07-15-03, 02:11 PM
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Any answer obtained using a clamp on ammeter/multimeter will likely be very far off. Motors present an inductive load and can have power factors as low as 0.1 to 0.2 depending on the load. With a pump the head and pipe friction are the main portion of the load. A restricted input to a centrifugal pump results in less power being drawn as the fluid just runs in a cicrle with the impeller. As the load on the motor changes, the power factor changes. Using 500 W per HP will probably still overestimate, but is a more likely value than 1 kW. Be glad yo do not pay for the lousy power factor like industry does.
Old 07-17-03, 09:26 AM
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In simple terms, a 1 HP motor at 0.8 power factor is about 1.2 kW. 1.2 kW * $0.85/kW-hour = 10.2 cents/hour = $2.45 per day = $73.50/month. You can get a timer for that that'll set you back about $75. If you run the pool pump 12 hours a day the timer will pay for itself in two months.

My $.02.


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