When you consider how much rain falls on and around the average North American home during the course of the year, it is no surprise that many homeowners have highly active sump pits. Others are fortunate enough to live in a location that drains well, and they rarely hear their sump pump working. Regardless of which situation you find yourself in, it is important to make sure that you have a sufficiently powerful sump pump in your basement.
Choose an extremely wet, rainy day, when the ground is saturated with water, to measure the water coming into your sump pit.
On an extremely wet, rainy day, run your sump pump until the water recedes to the shutoff level. Wait for 1 minute with the pump off, and then measure how far the water rose during that minute.
Since typical sump pits measure approximately 18 inches in diameter (check yours to verify), every inch of water inside the pit amounts to approximately 1 gallon. Multiply the number of inches that the water rose in a minute by 60, in order to estimate the volume of water that would come into your pit during an hour of steady rain.
Multiply this number by a "safety factor" of 1.5 to figure out the pumping capacity you need.
- A sump pit receives 20" of water in 1 minute, or approximately 20 gallons.
- Multiply: 20 gallons x 60 minutes x 1.5 = 1800 Gallons per Hour (GPH) capacity needed
To best protect your basement, get to know your sump pit intimately. Measure the water inflow into the pit many times, in the wettest conditions, to make sure you truly know how much water volume you could be dealing with.
Some homeowners, with especially active sump pits, decide to increase the safety factor. The best way to make that judgment is to simply know your sump pit. Perform the first step (measuring the sump water inflow) multiple times, especially in extremely wet conditions when the ground is saturated. You can increase the safety factor, but keep in mind that, if you get carried away and buy a much larger pump than you need, it will turn on and off very rapidly, which could cause it to wear out prematurely.
Finally, once you figure out the size you need and are shopping for your pump, you will likely encounter the term "lift." This refers to the height that the sump water must be pumped before leaving the house. For example, many basements are 7 feet tall, plus 2 feet into the sump pit, for a total of 9 feet of lift. Keep in mind that a higher lift distance makes the pump work harder, which will reduce its pumping rate.