Q. We are thinking about adding a waterfall to our small garden pond, but we wonder about the added electrical costs of running a pump 24 hours every day for 7 months a year. We are on a limited budget and don’t want to get stuck with big electric bills. Can you tell us how to figure out the monthly cost of running a pump? Would it be all right to run the pump only a few hours each day?
A. Determining the electrical usage and cost of a water pump is a very simple task. First, look on the pump housing (or on the box it came in) for information on electrical usage. You will see information on voltage, amperage and, perhaps, wattage. It is the amperage that determines the cost of operation.
If there is no wattage information, just multiply the voltage rating times the amperage rating. For example, except for very large, heavy-duty pumps, most pumps use standard 115-volt power sources. If the amp rating is 4, the wattage used will be 4 times 115, which is 460 watts. (Some heavy-duty pumps use 220 volts. In this case, a 4-amp pump would use 880 watts.) If the wattage is already on the pump, just use that value.
Electricity is sold by the kilowatt-hour. That is, the amount of watts used in units of 1000 for each hour. If our hypothetical 115-volt, 4-amp pump is run for 24 hours a day, it would use 460 watts times 24, or 11,040 watt-hours. Over the course of a month of 30 days, 331,200 watt-hours would be used. Dividing this number by 1000 yields 331.2 kilowatt-hours per month.
The accompanying graph (“Pump Electrical Consumption”) will save you the calculations. If your pump lists wattage use the left-hand axis. Locate your wattage and move horizontally across to the graph line. From the line move straight down to the bottom axis and read the kilowatt-hours used per month. If your pump lists amperage, use the right-hand axis instead and follow the same procedure.
Next, check your electric bill and find the cost of electricity per kilowatt-hour. If the bill does not state this directly, call your utility company and ask for the total cost per kilowatt-hour. Here in New England it averages about 10 cents, but in other parts of the country it may be as low as 5 cents per kilowatt-hour.
Lastly, multiply the cost times the estimate of your pump’s monthly kilowatt-hour usage. Assuming an electric rate of 10 cents per kilowatt-hour, our hypothetical pump would cost 0.1 times 331.2, or $33.12 per month to operate. Not cheap, huh?
Armed with this information, you can now compare pumps of equal pumping power in terms of their operating costs. Over the long term it might be less expensive to purchase a more expensive pump that is more energy efficient. Let’s see why.
Consider two pumps: Red and Blue. Red pump costs $50 but is a fairly inefficient design that uses 210 watts. Blue pump costs $100 but uses about 70 watts. The difference of 140 watts works out to 100.8 kilowatts per month, or about $10 per month. Thus, Blue pays for its higher price relative to Red in just five months, and from then on it will save you money. If the pump lasts three years, the total savings will be $312!
In a future issue of AFI I will discuss the many factors that go into choosing the correct pump for a pond system. Electrical usage is one very important consideration.
Yes, you can save money by running the pump only a portion of each day, and this is fine if the only purpose of the waterfall is ornamental. However, if the pump feeds a biological filter or is needed for aerating the water, then it must be run continuously.