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Horsepower vs. Gallons Per Minute

A lot of motor powered tools and appliances are rated by horsepower. The technical definition of horsepower is, horsepower is a unit for measuring the power of motors, one horsepower equals 33,000 foot pounds of work per minute. A foot pound is the amount of energy required to raise a one pound weight a distance of one foot.

What does all that mean? If you were an engineer you would be familiar with a formula that could chart the efficiency and recommend the best product for the job. For the average Joe or Jim, more horsepower means more power, which is not always the case….

In terms of sump pumps we look more at gallons per minute and hour more than at horsepower. Most sump pumps are rated by horsepower, but are also rated by gallons per minute and gallons per hour. Every pump has a performance curve that is based on the gallons per minute on the horizontal axis; and the vertical lift which is also called total dynamic head on the vertical axis. (Please see below for examples of various pump curves)

Pump Curve Example 1

Pump Curve Example 2

Most 1/3 horsepower sump and effluent pumps will deliver between 35 and 50 gallons per minute at 10 feet of vertical lift or total dynamic head. There are 1/3 horsepower effluent pumps that will pump 60 gallons per minute at a 10 foot total dynamic head. I can also site examples of pumps that are rated at ½ horsepower that will pump less than 70 gallons per minute. The actual performance has to do with the RPM of the motor, the amount of copper or metal in the motor, the size of the impeller and the design of the pump volute (the pump base or case).

What does this mean? Well, it means don’t purchase a sump or effluent pump based on horsepower, look at the gallons per minute or gallons per hour first. Then I suggest looking at how much electricity or the amp hour rating the pump has. The lower the amp rating the more efficient, or less energy will be consumed.

There are now sump pumps on the market that are equipped with a PSC motor, a “Permanent Split Capacitor” that are very efficient and can consume up to 40 or 50% less energy and deliver more gallons per minute or gallons per hour than ever before. (Please see our specifications for model # PZM-EP-33V-SJ

How much can you save with an energy efficient sump pump? If the average cost per kilowatt hour is $0.12 and your pump runs for 5 minutes per hour year round you could save as much as $50.00 a year. (Please see The Definition of Green is Pro Series Pumps)

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