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Five Quick Steps How To Size A Sump Pump

An Accurate Way To Calculate The Best Sump Pump Size For Your Pumping Needs

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Pictured are Steps to how to size a sump pump


Quick Info On How To Size A Sump Pump

Installing the right size sump pump is important. Too small of a pump leads to basement flooding and too much horse power causes a sump pump motor to turn on and off too quickly and wear it out faster.
Pictured is a sump pump system that you wish to learn how to Size
Here's the Quick Way to size a sump pump: only five steps.
The most accurate predictable way to size a sump pump is known as the Measurement Method. It takes 7 steps and some measurements and calculations.
Another approach for the less ambitious is the Eyeball Method which leaves some unanswered questions. This is watching what happens and see if your existing pump keeps up with the water entering the pit during heavy rainstorms and if it does assume the existing pump is right sized.
The most unpredictable method is believing what others say and assuming your water pumping needs fit their description. This is the Word Of Mouth Method and highly unreliable.
We recommend the first approach (measurement method) and present the 7 detailed steps below.
Why put your basement at risk to flooding potential when you can measure exactly what is needed?

How To Size Sump Pump Table Of Contents

Quick Info About How To Size A Sump Pump
The Five Step Quick Method - How To Size A Sump Pump.
The More Accurate Measurement Method
Eye Ball Method For Choosing The Right Size Sump Pump
Word Of Mouth Method
Common Questions About How To Size Sump Pump

Quick Five Steps How To Size A Sump Pump

In A Hurry? Do The Following Five Steps To Right Size A Sump Pump.

1) Measure the diameter of the basin.
Pictured measure the basin diameter.
2) Measure the water height when the pump is OFF and ON.
3) Count the number of pump cycles in one minute.
4) Multiply Step 2 By Step 3.

5) If basin diameter is 18 inches wide multiply by one. If basin diameter is 24 inches wide multiply by two. This is the GPM your sump pump needs.

Additional facts: One inch water height in an 18 inch wide sump basin equals one inch. In a 24 inch wide basin one inch height equals two gallons. If you know your sump pump model number, check the manufactures specs for the float ON and OFF height. Use this instead of measuring the water height. To get GPH multiple Step 5 by 60. To accomodate unkown factors, add an additional 10% to the GPM in Step 5.

There are other factors to consider so it is best to continue reading and learn about the measurement method. It is important to know how high the water must be pumped plus how many elbows are added to the discharge pipe system.

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How To Size Sump Pump Guide

Learning how to size a sump-pump is very important. If the horsepower is too small it will not keep up with the water entering the pit and the basin will overflow. If it is too large, the-basin water will be removed too quickly and the motor will short cycle shortening its life.


Factors Affecting Sump Pump Sizing

Basement sump pump sizing is affected by the following five factors: 1) Height of the-basin 2) Diameter of the-basin 3) Vertical height of discharge pipe from pump port to horizontal pipe leaving the house 4) Number of elbows and check valves in discharge pipe system 5) Rate of water-flow into the-basin during heavy rains.

There are also non sump pump system related factors such as house perimeter measurements, landscape slope around the house, roof slope and size, soil type and water table height.


Sump Pump Sizing Calculator

This is the Measurement Method approach.

Take the time to measure important aspects of your sump pump system so you have accurate results and really know what size sump pump is needed for your water pumping needs.

The following steps take the above mentioned factors and create a sump pump sizing calculator. Following these seven steps will help you to choose the best sump-pump horse power and pumping performance needed.

  1. 1) Measure The-Basin Height
  2. 2) Measure The-Basin Diameter
  3. 3) Find The Height Of The Vertical Portion Of The Discharge Pipe
  4. 4) Count The Number Of Elbows, Their Degrees, And Check Valves
  5. 5) Identify The Water Flow Rate Entering The Pit During Heavy Rains
  6. 6) Perform The Actual Calculation
  7. 7) Find A Sump-Pump That Can Handle The Water Flow Rate At The Measured Vertical Height

Step One: Measure The Height Of The Basin

Take a yardstick and rest one end on the bottom of the pit. Check the number of inches to the top which is at the basement floor level. This is the height of the-basin.
Step One: Measure The Height Of The-Basin

Step Two: Measure The Diameter Of The-Basin

Take a yardstick and lay it across the top of the pit. The distance from one wall to the other is the diameter of the basin. The most common diameter is 18 inches. Some are 24 inches. A 24 inch diameter is wonderful because two submersible sump pumps fit easily on the bottom. If a battery backup is attached in-line with the discharge-pipe or a water powered sump-pump is used, three pumps will easily fit.
Step Two: Measure The Diameter Of The Basin

Step Three: Measure The Vertical Height Of The Discharge Pipe

Take a sturdy tape measure. Stick it into the pit resting one end on the-basin bottom. Measure straight up until the highest point of the discharge pipe is reached. Do not be concerned about the bends or slopes at this point.
Step Three: Measure The Vertical Height Of The Discharge Pipe

Step Four: Count The Number Of Elbows, Their Degrees And Check Valves

Look for the number of connectors inserted into the discharge pipe as it is angled to go to the outside of the house. Record the degree angle of each connector. Count the number of check valves inserted into discharge pipe. Every system should have at least one check valve. A check valve prevents the motor from re cycling the same water over and over because when the motor stops some water remains in the discharge-pipe and because of gravity will flow back into the pit which could be enough to cause the motor to run again. This will cause short cycling and a shortened motor life. If more than one check valve, one ninety degree elbow and one 45 degree elbow are used, enough friction could be caused to one-half foot to the vertical discharge-height.
Step Four: Count The Number Of Elbows, Their Degrees And Check Valves

Step Five: Measure The Water Flow Rate Into The-Basin

Check the sump-pump manual to identify the pump motor ON point and OFF point. For example, let's say the manual says ON is 7 inches and OFF is 3 inches. This means the motor runs after 4 inches of water enters the pit and during heavy rains keeps running every time four inches of water enters the-basin.
Step Five: Measure The Water-Flow-Rate Into The-Basin

Use your watch digital reading or a time piece second hand to see how frequently the motor runs in one minute during heavy rainstorms. For example, let's say the motor runs every 10 seconds.

Now take the above measurements and put them all together to calculate the water flow rate and pumping performance required. We are using a discharge-pipe diameter of 1-1/2 inches (1.5-in.). A smaller diameter cannot handle the same volume. Likewise a larger diameter can handle more volume.

  1. 1) The-basin diameter. Let's say it is 18 inches.
  2. 2) The vertical height of the discharge-pipe. Let's say it is 9 feet.
  3. 3) The ON OFF point. We found it to be 4 inches based on the manufactures specifications.
  4. 4) The number of times the pump-motor runs during 60 seconds. This is every 10 seconds.

Step Six: Perform The Actual Calculation

The actual calculation is as follows.

  1. 1) An 18 inch diameter pit converts to one inch equals 1 gallon of water. A 24 inch diameter converts to two inches and equals 2 gallons of water.
  2. 2) In the example we are using, the sump-basin is 18-inches in diameter so every 10 seconds 4 gallons of water is pumped. This equals 6 runs during a 60-second interval. Four gallons times six equals 24 gallons per minute.
  3. 3) The sump-pump must have a pumping performance of 24 GPM at a 10 foot vertical height

Step Seven: Find A Sump-Pump To Handle The Water-Flow-Rate At The Measured Vertical Height

At a minimum, manufacturers provide the following information.

  1. 1) Float Switch ON and OFF point. Vertical float-switches attached to the sump-pump come preset and cannot be altered by the home owner. Tether float-switches do allow around a three-inch variance for setting. The best solution for customizing the ON and OFF point, is installing the HC6000 switch controller which allows customizing both the ON and OFF point. We installed the HC6000 in 2011. It has never failed and is still working perfectly. This was the best decision we ever made because float-switches fail. The HC6000 is not only extremely reliable but has a lifetime warranty. Read more about the HC6000 Sump-Pump Switch.
  2. 2) Pumping performance curve at various vertical heights. The vertical heights of 0-feet, 5 feet, 10 feet, 15 feet and 20 feet are most common.

Use the documentation provided by the manufacture if you want to find the right size sump pump for your pumping needs.

Manufacturers specifications, pumping performance curve and manuals for popular sump pumps can be found at SumpPumps.PumpsSelection.com.

How To Size Sump Pump TOC

Watch How Zoeller Explains How To Size A Sump Pump

Zoeller Pump Company presents a lot of detail in the following video. As you will see there is a lot that goes into choosing the right size for a sump pump.


Measurement Method Summary

Learning How To Size A Sump Pump is easy if you do the steps prescribed above. The key steps are: Make sure you know the measurements of your sump-basin, the vertical height of the discharge-pipe, and the distance between the float-switch ON and OFF point. Take those measurements to calculate the water flow rate into the sump-pump-basin. Check the manufacturing documentation to find the right size pump. Installing the right size sump-pump is very important to preventing both flooding and motor burn out.

Manufacturer's documentation is readily available at Sump Pumps . Pumps Selection . Before purchase your next sump-pump, make sure you have the right size.

How To Size Sump Pump TOC

Eyeball Method Of Sizing A Sump Pump

The Eyeball Method of sizing a sump pump is much less involved; but also less accurate.

There are seven steps to the Eyeball Method.

1) The next time it rains heavy continuously, watch how close the water gets to the top of the basin before the pump runs.
2) Determine if the basin almost overflows or there is very little water flow and the pump keeps up with the water influx into the pit very easily.
3) Identify the vertical height the water is pumped to before leaving the house
4) Identify the brand and model number of your existing pump.
5) Go to the manufacturer's website and download the performance curve for your pump.
6) Find the GPM (gallons pumped per minute) or GPH (gallons pumped per hour) for the discharge pipe systems vertical height.
7) The GPM or GPH determines the pumping performance a sump pump must have to meet your need.

Eyeball Method Summary For Sizing A Sump Pump

Using the Eyeball Method certainly takes less time, but the knowledge gained about your sump pump systems is very limited. At least you know how much water your current sump pump can handle and what size of sump pump to install in case your existing sump pump needs replacement. But we would highly encourage you to take the Measurement Method approach sometime in the near future so you have a much better understanding of your system, its capability and its flexibility to meet higher pumping demands in the future.

How To Size Sump Pump TOC

Word Of Mouth Method Of Sizing A Sump Pump

The Word Of Mouth Method of sizing a sump pump is very unpredictable and highly inaccurate.

The Word Of Mouth Method assumes the information heard resembles your situation. But just because a neighbor needs a one-half horse power pump does not mean your property needs the same.

The water table, subsoil, house perimeter and roof size, and the landscape around the house in the same neighborhood may be different. Therefore to be prepared for those heavy rainstorms it is important to at least perform the Eyeball Method and to have the most peace of mind, perform the Measurement Method.


How To Right Size A Sump Pump Conclusion

Using a sump pump that is right sized is key to having peace of mind during the rainy season

Cleaning up a flooded basement certainly takes much more energy and costs more than taking the time to do the Measure Method so you have the right size sump pump installed

The quick way fo choose a right size sump pump is only five steps. 1) Meausere the pit diameter. 2) Identify the distance between the pump ON and OFF point. 3) Count how many times the motor turns on in one minute. 4) Multiply Step 2 By Step 3. 5) You are done. This is teh GPM an installed pump must handle for your water pumping needs.


Enjoy peace of mind knowing sump pump can handle the unpredictable, heavy rains that have increased in intensity and frequency these past few years.

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Questions About How To Size A Sump Pump

Do I Need A 1/3 or 1/2 HP Sump Pump?

A 1/3 HP sump pump is most commonly used. A 1/2 HP sump pump is most commonly needed for those houses that are found in a high water table area where the sump pump runs even when it is not raining. A house at a lower elevation than those in their neighborhood or those located in a lower elevation subdivision may be best using a ½ HP sump pump. A ½ HP sump pump can handle around 35% more volume of water per minute or pumping. In an hour's time the difference is significant.

How Do I Size A Sump Pump?

Simply put. Know the diameter of your basin. One inch equals one gallon pumped in an eighteen inch diameter pit. For a twenty-four inch diameter pit, one inch equals 2 gallons of water pumped. Measure how many inches of water is pumped each time the pump runs. Then multiply the number of inches times the number of times per hour to get the pumping performance GPH required.

Can A Sump Pump Be Too Powerful?

Yes, a sump pump can be too powerful. Too powerful of a sump pump will be pumping in short spurts which is a lot of stopping and starting for the motor leading to unnecessary wear and tear. Plus the float switch will also experience more wear and tear.

Is 1/2 HP Sump Pump Too Much?

A 1/2 HP sump pump can be too much if water just runs slowly into the pit and it takes over 2 minutes before the pump cycles during a heavy rainstorm. There is no advantage of having a 1/2 HP pump when the need is that low. A 1/3 HP pump will cycle better without putting so much stress on the motor frequently recycling. If the pump runs less than every 2 minutes a 1/2 HP would be appropriate.

How Much Water Can A 1/3 HP Pump?

The amount of water a 1/3 HP pump can remove ranges from 42 GPM to 76 GPM based on suction type. Top suction pumps can remove more water per minute but are not designed to handle solids.

How Far Can A 1/2 HP Pump Push Water?

A 1/2 HP sump pump is designed to easily pump water 10 feet up from the basin bottom, through vertical discharge piping and away to its destination. The length at which the pump will no longer be able to pump ranges from 19 feet to 26 feet.
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