Pump Sizing Guide
Learn how to size your pump correctly for your application

How do you know what size or type of pump you need? There are some basic questions you can answer to help you decide. For instance, how much water needs to be pumped and how quickly does it need to be removed? What is the total distance from beginning to end that the discharge piping will travel from the pump? What is the total vertical rise from the pump to the highest point of the discharge piping? Is the water clear or does it have leaves or other stuff floating in it? We will provide information about pump characteristics and what to specifically look for when you are trying to determine which pump will best meet your needs.

While we cannot guarantee that a certain size of pump will be appropriate to your situation, we can offer some guidance on basic sizing. If you aren't sure exactly what your pump needs are, it might be best to consult a local licensed plumber before you start shopping. They may have recommendations or be able to advise you about certain requirements for your area. And as always, if you have questions about any specific model of pump we offer, you can always contact us for more information.

Solids Handling

Are you pumping clear water or does your water have some junk in it like leaves or twigs or other debris? Pumps for clear water usually cost much less than pumps made for handling solid type waste in water. If you are pumping clear water then a normal sump pump is all you will normally need. If you have small bits of debris in your water then a sump/effluent pump would be a step up and will move water with 3/8", 1/2" or 3/4" spherical solids (depending on the pump chosen for your application) through the pump without clogging the discharge. If you have leaves and possible larger particles in your water then you will need to look into sewage ejector pumps because they have the ability to push water and handle up to 2" spherical shaped solid waste materials.

DuraMAC sump pumpSump Pumps
for clear water
Little Giant sump effluent pumpSump/Effluent Pumps
for 3/8" - 3/4" solids in water
sewage ejector pump by Little GiantSewage Ejector
for up to 2" solids in water

Shut-off (aka Vertical Lift or Maximum Head)

The shut-off distance of the pump can be a very important often overlooked detail. The shut-off height is the highest point vertically the pump can lift liquid. At this maximum shut-off height the pump can be on and pumping but the liquid will not move beyond that height in the pipe. The maximum shut-off distance is normally provided in the pump curve chart of each individual pump and shown as total dynamic head. Total dynamic head (TDH) is determined by two factors, static head and friction loss. Static head is calculated by measuring from the minimum water level the pump can operate (where the water enters the pump) to the highest point of the discharge piping. Friction loss is the resistance to the flow of water caused by the discharge piping material, type of valves and number of directional fittings used like 90° or 45° elbows. Since plastic piping is the most common discharge piping used, we offer friction loss charts for plastic piping and fittings to help you determine the friction loss of your application. Static head and friction loss are added together to equal the total dynamic head.

Performance Curve & GPM

Performance curve charts are provided for every individual pump to show the working range of the pump. These charts show a graph of how many gallons per minute (GPM) and/or liters per minute (LPM) liquid will flow at a given discharge piping height. These charts are very useful to help you determine the size of pump you may need. You normally want the liquid to flow at the fastest rate possible at the discharge height your installation requires. This is why it is important for you to know the distance of the total vertical rise from the pump to the highest point of the discharge pipe. The higher your vertical rise, the slower your gallon per minute flow rate will be. The lower the vertical rise the higher the gallon per minute flow rate will be. When you are comparison shopping different pumps be sure you are comparing the GPM flow rates of the pumps at the same height level. For example, one pump may be rated at 120 GPM at 5 ft. of head but the other pump might be rated at 100 GPM at 10 ft. of head. But if you check the performance curve chart you may find the 100 GPM at 10 ft. of head actually is 130 GPM at 5 ft. of head which would be a slightly higher pumping advantage.

Horse Power (HP)

Horse power is a unit of power given to rate a specific work being accomplished. Horse power ratings for electric motors are normally calculated using torque and speed. In the case of pumps, this rating must also include the size of the impeller to be used to push water. Many manufacturers use different methods to determine horse power ratings for their pumps and there is not always a direct electrical association to this horse power rating. We have found that most manufacturers use the performance curve chart as the association to their horse power rating without adding the electrical current draw to their equation. In other words you should compare the solids capacity, the performance curve charts and the electrical amperage when shopping for residential and smaller commercial grade sump pumps, effluent pumps and sewage ejector pumps. Naturally we all tend to think bigger is better, but that is not always the case when choosing a pump. Of course the higher the HP rating for a pump the stronger its pumping capacity will be. However, having a larger horse power pump than you really need can lead to premature pump failure. Most of the wear and tear on any pump is the start up of the pump and the heat generated by the motor windings. Heat dissipation is extremely important to keep your pump motor cool and oil filled motors help dissipate heat off the motor quicker than air filled styles. The longer the motor is allowed to run the more the windings can cool off. So if your pump is starting and stopping too often because the pump is too big for your application you may need to replace it sooner than you wish.

Amps & Volts

When comparing pumps compare the amperage. The lower the amp rating the better. Lower amp usage means less energy is used to run the pump and that is money in your pocket. Most pumps are available in 115 or 120 volts which will plug into a standard electrical outlet and some are also available in 230 volt or 208-240 volt versions. Pumps with 230 volts or 208-240 volts oftentimes use less amps to run them but then your building electrical wiring must be compatible with the pump voltage. Make sure the breaker in your electrical panel has a large enough amperage rating to handle the electrical draw of the pump you intend to purchase. If you are unsure we suggest you contact a licensed electrician and have them check the capacity of your electrical panel.

Finding the right pump for your application isn't impossible and hopefully, we've helped you determine the questions you need to ask when sizing your pump. Remember to mark down your performance and height needs before beginning shopping so that you can find the right pump for your application.

You may also be interested in:

return to top ↑

Copyright© 1995-2024 PlumbingSupply.com.
All Rights Reserved.