Informational Guide

What Size Sump Pump Do I Need?

by Andrew

During heavy rainfall or flooding, sump pumps provide the best and effective ways to save your house from destructive water damage.  

Though there are many factors that you should consider when purchasing a pump, the most critical among all is choosing the right-sized sump pump. 

Wondering what size sump pump do you need? If so, then read on! 

Are you seeking sump pumps with higher horsepower and better performance than your existing ones?  

So, what size sump pump to buy exactly? Here are some of the standard sump pump sizes and how much water they remove easily: 

1/3 HP Sump Pumps 

1/3 HP is the ideal sump pump size for homes with average water tables. It's the most common-sized sump pump available in the market that handles many water tables quite easily. 

1/3 horsepower sump pumps can smoothly handle about 8-11 feet vertical lifts off the pump, 90-degrees elbow, and horizontal pipes running between 4 and 26 feet.  

1/2 HP Sump Pumps 

½ horsepower is a perfect sump pump size for basements with above-average water tables. Typically, they remove 38 to 42% more water than their counterpart 1/3 horsepower sump pumps.  

Similar to 1/3 HP sump pumps, ½ sump pumps can also handle 8-11 feet vertical lifts off the pump, 90-degrees elbow, and horizontal pipes running between 4 and 26 feet.     

room

3/4 HP Sump Pumps 

3/4 HP sump pumps have a 20-25% more pumping capacity than ½ horsepower sump pumps. They can handle higher vertical lifts of 22 to 32 feet or/and horizontal pipes effortlessly running between 152 and 252 feet.  

Wondering when to consider ¾ horsepower sump pumps for the house? You can install a ¾ HP sump pump only if: 

  • the house is situated in a low-lying or floodplain area 
  • the water table is high in the area and is vulnerable to flooding  
  • the cellar is deep 
  • water is released using more than 11-feet of horizontal pipes  
  • you're utilizing the sump pump for external pumping  

What Size Sump Pump Do I Need? 

Learning the size of sump pumps is extremely important. That's because if the HP is extremely small, it won't sustain the incoming water. As a result, the basin will spill over. On the other hand, if the HP is too big, it will quickly remove the basin water, affecting the motor.  

Want to know what size sump pump do your need? Here are a few steps on how to calculate the sump pump size:  

Measure The Basin Height And Diameter 

To measure the basin height, all you have got to do is grab a measuring stick and place its one side underneath the pit. Then, check the inches at the cellar floor level, and that's all.  

Now that you know how to calculate the basin height, here's how to measure the basin diameter: 

Take a measuring stick and place it above the top surface of your sump pit. Next, calculate the distance between two walls is the basin diameter. One of the most common diameters is 18-inches; however, some diameters are 24-inches as well.  

Find The Height Of The Vertical Portion Of The Discharge Pipe 

Take a lengthy and sturdy measuring tape. Stick the tape into the sump pit by placing one side at the bottom of the basin. Now, start measuring! 

Take it all the way up till the highest spot of a drain pipe reaches. Don't worry about the slopes or bends at this stage.  

Count The Number Of Elbows, Their Degrees, And Check Valves 

Please search for the connectors inserted in the drainage pipe as it's angled outside the house. Make sure to record all connector's degree angles and count the check valves placed in the drain pipe.  

Keep in mind that all systems should have a minimum of one test valve. Check valves prevent motors from recycling water again and again.  

This is important because when the device shuts off, some water stays in the drain pipe and gets back to the sump pit due to gravity, causing sump pumps to operate again.  

If this happens constantly, it will cause short-cycling, which will reduce the life span of the motor.   

Identify The Water Flow Rate Entering The Pit During Heavy Rains 

Check the pump manual to determine the sump pump motor "off point" and "on point." For instance, suppose the manual states "OFF" is "3-inch" and "ON" is "7-inch".  

We use a drain pipe diameter of 1.5 inches. Smaller diameters can't handle a similar volume. Likewise, larger diameters can easily handle a lot more volume.  

  • Let's say the basin diameter is about 18 inches 
  • Let's assume the discharge pipes' vertical height is about 9 feet 
  • The "On/Off" point is 4-inch depending on the manufacturer's specs 
  • How many times does the sump pump motor function in a minute? Let's say every 10-second 

Perform The Actual Calculation

Here's how the accurate calculation works: 

  • An 18-inches diameter sump pit converts into 1-inch, which equals 4.5 liters (or one gallon of water). A 24-inch diameter converts into 2-inch equals 9 liters (or 2 gallons of water) 
  • As per the case we use, the sump basin's diameter is 18-inch, which means every 10-second, 18.1 liters of water (4 gallons) is pumped. It equals six (6) runs in a 60 seconds interval. So, 4 gallons times 6 equals 24. Hence, 24 gallons/minute 
  • The sump pump should have a removing capacity of about 24 GPM (Gallon Per Minute) at 10 feet vertical height 
sump pump hole

Sump Pump Sizing Chart (By Pit Diameter) 

Since the sump pit measures approximately 18-inch in diameter, water within the sump pit equals one gallon.  

Now, multiply the inches of water accumulation by 60 to measure the quantity of water coming to your sump pit in one hour of constant rain.    

Multiply the number you get with 1.5 to determine the sump pump size you need. To help you choose the best, here's the sump pump sizing chart by pit diameters: 

Pit Diameter 

Gallons Of Water 

72 inches 

17.5 

60 inches 

12 

48 inches 

7.5 

42 inches 

6 

36 inches 

4 

30 inches 

3 

24 inches 

2 


Other Things To Consider When Choosing A Sump Pump Size 

Since the sump pit measures approximately 18-inch in diameter, water within the sump pit equals one gallon.  

Now, multiply the inches of water accumulation by 60 to measure the quantity of water coming to your sump pit in one hour of constant rain.    

Multiply the number you get with 1.5 to determine the sump pump size you need. To help you choose the best, here's the sump pump sizing chart by pit diameters: 

Sump Pump Type 

Here are some of the most common types of sump pumps you can choose from: 

  • Submersible sump pump 
  • Pedestal Sump Pump 
  • Water-Powered Sump Pump 
  • Battery-Backup Sump Pump 
  • Combination Sump Pump 

The Right Horsepower Motor 

If you've moderate-to-low water accumulation in your cellar, a 1/3 horsepower sump pump will suffice.  

But, if your cellar is vulnerable to heavy rains or flooding, you should choose more powerful sump pumps such as one horsepower.  

Existing Piping  

Another crucial thing you'll have to consider when choosing the right sump pump size is the vertical and horizontal distance the pump motor will require to push water.  

For example, a vertical drain line needs a higher horsepower sump pump to work against gravity. Therefore, the bigger the vertical lift, the higher the HP motor required.  

If the pump doesn't have adequate power, it won't push water upward and cause a deluge.  

The Vertical Lift Or Static Head 

To stop water from coming to your home, you should consider all crucial vertical lifts. Wondering what that is? 

Vertical lifts, also called static heads, are the height water needs to move as it travels through the discharge pipe. Remember, substantial heights can discharge a low-efficiency sump pump. 

If you've got a sloping backyard or intend to pump water all the way upwards, you'll need a bigger HP pump to overtake gravity. Under such circumstances, the sump pump works harder to minimize the pump rate.  


People Also Ask (FAQs)

What is the sump pump wire size? 

The wire sizes vary based on the sump pump's HP ratings and volts. So you'll have to use the accurate gauge or length of wire as per the manufacturer's specs.  

Fragile wires may heat excessively while the sump pump operates, leading to a potential fire. However, if you use the correct wire size, nothing of this sort will happen.  

What size PVC pipe for the sump pump? 

Many sump pumps come with an embedded fitting for a drainage pipe, typically 1.5" or 1.25" inside diameter. Since most pumps discharge pipes are PVC, identify the internal diameter. The discharge pipes will be approximately 1.5-2 inches on the exterior.  

What size of a breaker is for a 1/2 HP sump pump? 

In most cases, the manual of your sump pump recommends the breaker size. Nevertheless, 15-ampere breakers are perfect for ½ horsepower sump pumps. Additionally, you can operate 12 American Wire Guage (AWG); however, if the function is extended, utilize a 14-AWG. 

Can you oversize a sump pump? 

There is a famous saying that bigger is better; however, the same isn't true with sump pumps. Over-sized sump pumps can give rise to continuous cycling and may cause your system's premature burnout.  


Conclusion

Sump pumps save your house from flooding and heavy rains by pumping underground water out of the crawl space or basement.  

Amongst the many crucial factors to consider when purchasing a sump pump, size matters the most! The wrong-sized sump pump won't drain the water out of the house smoothly and may burn out untimely.  

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