How They Work, Types, and More

19 Aug.,2022


Vertical Centrifugal Sump Pump

Vertical Centrifugal Sump Pump

What is a sump pump?

A sump is a low space that collects liquids. Your car, for instance, has a sump to collect oil. In the same way, homes have a small pit that’s dug into the floor of the basement to collect water that filters through the loose earth surrounding your foundation.

A sump pump is a simple device that detects water in the sump and moves it away from the property through a network of pipes. Check out this video for a simple explanation of how a sump pump works.

Sumps are usually 2 feet deep and 18 inches in diameter. When the water rises to a certain level, a floating switch completes an electrical circuit and engages the pump. Systems usually contain a one-way check valve which prevents expelled water from flowing back into the pit.

Many sump systems have alarms to alert the homeowner if water rises past a certain point, indicating that the sump pump is failing. Modern smart pump alarms can even send alerts right to your phone. There are also sump pump alarms that indicate the backup pump has engaged, meaning you should check the primary pump (more on primary and backup sump pumps further down).

Sump pumps require electricity. Since they’re operating near (or in) water, it’s important that the outlet you connect the pump to has a ground fault circuit interrupter (GFCI). You should also connect your sump pump to a back-up power source. Flooding often accompanies severe storms, which often cause power failures. If your sump pump detects water but has no power to operate, it’s going to have a hard time protecting you from water damage.

Types of sump pumps

Sump pumps are either primary or backup, and your system should have one of each. Primary sump pumps do most of the work most of the time. The backup sump pump is only there to tag in if the primary pump fails, or if it can’t keep up to the water inflow.

There are two main types of sump pumps: submersible and pedestal. Either type can come in primary or backup variety. You can also divide backup sump pumps based on their backup power source: battery or water.

Submersible pumps

Submersible sump pumps are bulky devices. They sit right inside the sump pit, and function while underwater (hence, submersible). Since they sit in a pit, they run quieter than pedestal pumps, but are usually more expensive. They’re also harder to access for maintenance.

Pedestal pumps

Pedestal pumps are long, upright devices with the pump motor sitting on top and the intake device, or impeller, at the bottom. The motor on a pedestal pump isn’t meant to get wet. These are less expensive and easier to access for repairs compared to the submersible variety, but some plumbing experts consider them less reliable than submersible pumps. They’re also louder, as the motor sits above the sump pit.

Battery operated backup

The most common type of backup sump pump is the battery-powered backup. These don’t replace a primary pump. Instead, they spring to life when the primary pump cuts out due to a power failure or some other reason. Most often, they’re connected to a large battery (like a marine or car battery).

Water powered backup

Water powered backup sump pumps aren’t connected to an electrical current; they’re powered by good, old-fashioned water pressure. They have the advantage of unlimited runtime, but there are some restrictions. Water-powered pumps need a strong, steady flow of water, like the high-pressure flow of a city water system. In a home with low water pressure, or pump-powered well sources, water-powered sump pumps won’t work correctly. They’re also more challenging to install than their battery-powered counterparts.

Combination sump pump

It’s also possible to buy an all-in-one sump pump that includes a primary pump and a backup pump in the same package. It may be more cost-effective than buying each separately, but they tend to be large and may not fit in smaller sump pits.

What size pump do I need?

Sump pumps come in a variety of outputs. Each pump comes labelled with a reference chart explaining how much water it can displace.

The chart contains two columns: head refers to the vertical distance that water must travel from your sump pump to the outlet pipe, and flow refers to the volume of water that the pump can displace (in gallons per minute).

These figures are inversely proportional; for any given pump, the flow reduces as the head increases. That’s because the pump must work harder to push the water further up, thus decreasing its efficiency.

Determine flow rate

To figure out your flow rate, wait for a rainy day and run your pump until the water drops below the shut off level. Then, disconnect the pump from all power sources and measure the distance the water rises in one minute. For an 18-inch sump, one inch of water is equal to one gallon. In a 24-inch sump, one inch of water is equal to two gallons. Once you’ve calculated the flow rate, multiply it by 1.5 to allow a margin for severe storms.


Next, measure the vertical distance from the bottom of your basement to the outlet pipe. The outlet is usually at or around ground level. Then, reference the chart on your pump to see if the flow rate is sufficient for the head distance.

Experts recommend a power rating of 1/3 horsepower for average homes. Take into account elbow joints, narrow pipes and check valves as well; these increase friction, potentially requiring a more powerful pump. If you’re in any doubt, contact a plumber to determine whether your sump pump is sufficient.

Sump pump costs

A brand-new sump pump, on its own, runs between $100 and $500. Of course, that depends on the size and style; pedestal pumps are much cheaper than combination pumps, for example.

When you buy a new sump pump, the cost of the pump is just one piece of the puzzle—you also need to install it. If you don’t already have a sump pit in your basement, installation can be pricey. Expect to pay at least $2,500-5,000 to dig a new sump pit and install a pump if you’ve got a concrete basement floor.

How much does it cost to replace a sump pump?

If you already have a sump pit and you’re simply replacing the pump, the cost is much lower. If you’re comfortable doing the installation yourself, you won’t need to spend more than the price of a new pump, between $100 and $500.

If you have someone install your replacement sump pump, the average cost is around $500, including the price of an average pump.

Sump pump life expectancy

Finally, be aware of the life expectancy of your sump pump. Most pumps last around 10 years, but the lifespan is affected by the acidity and cleanliness of the water entering the pump.

Maintaining a sump pump

Sump pumps require scheduled maintenance. Dirt, sand, and other debris can clog the pump and prevent it from working at capacity during an emergency. Most homeowners only find out that their pump isn’t working when it’s too late; we recommend servicing your sump pump every 6 months.

The good news is:

If you’re handy, you can do most of the maintenance yourself. Check out for a simple guide or follow these steps:

  • First things first, make sure the pump is upright. The vibration of the motor often causes pumps to shift. If the pump is not sitting straight, the float arm can become jammed.
  • Check the GFCI outlet to make sure it’s plugged in and the cord is in good condition. If there is moisture present, the GFCI breaker may trip, causing the sump pump to shut down. If so, you’ll need to reset it.
  • Pour some water into the pit to test the pump. It should start automatically and drain the water away quickly. If not, have it serviced by a professional. While you’re testing the pump, go outside and make sure water is flowing through the discharge pipe.
  • Disconnect the check valve and remove any debris.
  • Check the backup pump’s battery. Periodically test the battery’s charge using a multimeter. If you can, connect a maintenance-free battery to your backup; an AGM (absorbed glass mat) battery is one of the best options for a sump pump.

If DIY isn’t your thing, call a professional to service your pump. They’ll ensure the pump is working at capacity and test the backup power source and alarm. They’ll also check the discharge line for clogging.

As well, consider installing a backwater valve to prevent your sewer line from backing up into your house. It’s also a good idea to remove debris from any drains, both inside your home and the municipal storm drains nearby.