The amperage rating of the pump motor times the voltage would be the wattage that the pump needs once it has started up. But an electric motor needs an initial surge of power to overcome inertia, called the “startup wattage,” and that larger number is what you should use. 

    Here’s the average startup wattage requirements for different sizes of submersible pumps:

• 1/2 hp - 2,000 watts
• 3/4 hp - 3,000 watts
• 1 hp - 4,000 watts
• 1-1/2 hp - 5,000 watts

    This is a generalization, and because of variable startup requirements of each specific pump and different ways that the power is regulated by each generator, it should be used as a rough guide only. We recommend double-checking with your local well contractor or electrician.

   You will want to add an allowance for a few additional appliances if the generator is for emergency power outage use, such as a refrigerator and lights, unless the generator will be dedicated only to the well pump or it will only be run with everything else off. Here’s some additional ratings:

• Box Fan - 115 watts
• Refrigerator/Freezer - 550 watts / 1350 startup watts
• Toaster Oven - 1500 watts
• Microwave - 625 or 1000 watts
• Coffee Maker - 1300 watts
• Lights - rating of bulb
• Space Heater - 1500 watts

    Also, always start the generator and have it up to speed before letting the well pump kick in. Conversely, turn off the well pump first before shutting down the generator to avoid damaging the pump motor; and this means be sure to avoid letting the generator run out of fuel while the pump is running.

    If you think a whole-house backup generator is what you need, click the link below to go to an easy to use Generator Sizing Calculator at the Generac® website.  

                                Generator Sizing Calculator

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Here’s links to a collection of our other blog posts about WELLS:

• What is the blue dumbbell-shaped tank at the well equipment?

• What is the tank marked "potassium permanganate" in the water treatment system for? 

• Does an abandoned well need to be capped or removed?

• Does a homeowner need a permit to drill a water well on their property in Florida? 

• Is a high iron level in well water a health hazard?

• How often should a well be disinfected? 

• Should I test my well water for arsenic?

• What is the danger of radon in well water? 

• Why would a well need to have a chlorinator/dechlorinator system? 

• Why does my well pump turn on and off every time I use water?

• What is the required water testing for an FHA, VA, or USDA mortgage application? 

    Visit our ELECTRICAL and WELLS pages for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.