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Question DetailsAsked on 7/10/2017

I am looking to find out how much it cost per month to run our septic tank lift pump.

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Not much - depends of course on your unit, but lets rough out an estimate - say for a low-lift (a few feet, not more than say 10') normal unit would be 1/2HP (so about 400- watts power draw) with an output of say 3000 gph gallons per hour). Normal household water use is 50-100 gpdpc (gallons per day per capita), so say 5 people in the house would be not more than 500 gpd down the drain, usually more like half that. (You can pro-rate these numbers based on number of people in house). A high-lift pump (say 20-30' of lift would likely be about twice the horsepower and similar flow capacity, if only lifting a couple of feet then output would be about twice so half the power usage per gallon, as an idea of the range of these numbers.

So - with say 500 gpd throughput, and assuming it runs twice as long per cycle as it takes to actually pump the rated amount of liquid (to include startup amperage draw and drawing a suction and a bit of after-run runoff time as the switch operates), you are talking probably maximum 10-20 minutes run time per day, or about 5-10 hours per month - which works out to about 2-4 KWHr/mo ((kilowatt hours/month).

[Note - a kilowatt hour = 1000 Watts for one hour - so a 1/2 horse motor pullling maybe 400W (there are about 800W total draw per horsepower, including line losses) = 0.4 KWHr of power, which is 0.4 KWHr per hour of running time.]

With nationwide average power cost of say $0.12/KWHr, that 5-10 running hours per month works out to about $0.24-0.48/month electricy usage for the 1/2HP 10 foot lift base case. Maybe more like half that if only a couple of foot lift to the leach field, maybe double that for a 10-30 foot lift or long pipe run to the leach field, maybe up to double again those numbers if in a real high power cost area, but that is the ballpark cost range for the power - almost certainly less than around $1-2/month for pretty much any normal case.

Now - things that can increase that - certainly inflow to the tank or the pump pit from irrigation or rainwater would increase that, but not likely more than less than 100% - unless you have a real high water table and have groundwater continually flowing into the septic tank, which could make the pump run almost continuously (and wear it out pretty quick - they are not made for long running periods).

A lift pump backflow check valve sticking open (not an uncommon thing) that allows backflow from the leach system to run through the pump back to the pump pit, so the pump is very frequently having to repump the same liquid to the leach field again and again, would certainly crank this number way up - potentially to the $15-30/mo range for the base case (double that for larger high-lift pump) assuming the same $0.12/KWHr electric rate and assuming the pump is actually running half the time. In a properly designed leach field system that could only happen, even if the backflow preventer were stuck open, if the leach field was saturated and backing up from excess slime buildup in the system. If backflow to the pump pit were the case, if you take a lawn chair and sit out near the pump where you can hear it and do some web cruising or read of book or such for an hour or more, you should certainly hear it kicking on and off fairly frequently even when water is not coming in from the house (so do this check when showers and washer and dishwasher and such as not in use - ideally when there is NO water use in the house to cause the pump to kick on).

If you suspect this as the source of a major power usage, you could also (with most units with a plug-in as opposed to hard-wired cord) plug it into a wattmeter (like a Kill-A-Watt meter rated for at least the motor wattage for about $20-30) to measure its usage over a day or two - though only if the plugin point is not real damp with "condensing" conditions (free moisture forming on surfaces in the area), as the wattmeter will not be made for those conditions and could short out. Though in those conditions, you might be able to (using a heavy-duty extension cord or two rated for 15A or more) run the pump cord to above ground to the watt meter (protected from rain) and then another cord back to the outlet to get the watt meter out of the damp conditions.

If this did not help, or it is running with any frequency when there is not water usage in the house, then Septic Tank would be your Search the List category to find a vendor to investigate this - be sure to get one who does septic system repairs, not just a company which only pumps tanks.

Answered 3 years ago by LCD

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