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Well Pump Checklist

So you need a well pump and you’re not a pump expert.  How can you even begin to look for a pump?

The first thing to know is what size (diameter) well you have.  Well pumps are typically available in 3, 4, 6, and 8 inch sizes.  Most residential well pumps are 3 or 4 inch.  Knowing this will narrow down your search tremendously.

Next, you need to know the electrical service you have available.  In the USA, typical residential service is single phase, 120 Volt.  This voltage can be a little bit confusing, as well pumps and other equipment and appliances are often labeled as 110V or 115V.  Actually, these are all equivalent.  The 110V and 115V items are intended to run on 120V service; they are simply rated to be able to operate on lower voltage.  

Other somewhat common electrical service possibilities are single phase 230V, three phase 230V, and three phase 460V.  

If you know these two bits of information (example:  I need a 4 inch well pump for single phase, 120V electrical service) you will be well on your way to selecting a pump.  Even if you intend to hire a professional to figure out everything else, these two items are essential to begin.

Of course, the entire reason you want a pump is to provide a flow of water at acceptable pressure to your home or for some other service.  

How much flow do you need?  One good way to determine this is to simply see what the existing pump (if there is one) provides.  Flow is measured in Gallons Per Minute (GPM), and pressure is either measured in PSI or in “feet of head”.  This will be expressed as “10 GPM @ 90 psi” or something similar.

If you don’t have an existing pump, or don’t know how much flow or pressure it provides, there are guidelines to follow.

The minimum recommended flow for any well pump is 5 GPM.  

There are two common ways to size a pump for flow for a residence:

1.  Add up the water using fixtures in the home, and have a flow in GPM equal to the number of fixtures.  For instance, if you have 2 sinks, 2 bath tubs, 1 kitchen sink, 1 dishwasher, and 1 washing machine, you would need a 7 GPM pump.  

2.  If you are concerned about having plenty of water at peak usage times (often the morning), you need to take into consideration how much water could be used at any one time.  For instance, showers typically use 5 GPM, so if you have two showers and want to be able to use both without any water shortage, you would need 10 GPM. 

Recommendations are as follows:

  • 1 Bathroom = 7 GPM
  • 1.5 Bathrooms = 10 GPM
  • 2 Bathrooms = 14 GPM
  • 3 Bathrooms = 17 GPM

Your exact situation may have different requirements, the figures above are simply general guidelines.

As for what pressure you need, your well pump needs to generate enough pressure to get water up out of the well and to your house, at the PSI you want at your house.  Maybe you want 60 psi available at your house.  Your pump will need to generate enough pressure to get the water out of the well PLUS that 60 psi to provide adequate service.  In order to determine how much pressure is required to get the water out of the well, you will need to know the depth of the well and the water level.  Also, if piping runs horizontally once the water is above ground, you will need to know how far that is.  With this information, along with the pipe size, the number of elbows, and the number of valves, filters, and other obstructions, a pump professional can calculate the psi of the pump that you need.