What a sump pump does
A sump pump sits in a pit (the sump) at the lowest point of a basement or crawlspace. Groundwater collected by drain tile around or under the foundation flows into the pit, and when the water rises, a float switch turns on the pump, which pushes the water out through a discharge pipe away from the house. In homes with high groundwater or drainage problems, a sump pump is what keeps the basement dry.
Do you need one?
Signs you might include water seeping into the basement or crawlspace after rain or snowmelt, a high water table, an existing drainage system with no pump, or a finished basement in an area prone to water. A contractor can evaluate whether drainage improvements outside, a sump system inside, or both are needed.
Types of pumps
- Submersible pumps sit in the pit underwater. They're quieter and common in finished basements.
- Pedestal pumps have the motor above the pit. They're easier to service but noisier.
- Pump capacity should match how much water flows into the pit and how high and far it must be pushed.
- Switches: vertical float, tethered float and electronic switches each have pros and cons. A switch that sticks is a common cause of failure.
Backup systems
Sump pumps fail most often when they're needed most: during storms, when power goes out. Backup options include:
- Battery backup pumps, which run when the main pump fails or power is lost. Batteries need periodic replacement.
- Water-powered backup pumps, which use municipal water pressure; they don't need electricity but use water and need adequate pressure.
- A second primary pump in the pit for redundancy.
- A generator with a transfer switch or interlock.
Alarms
A high-water alarm warns you if the water rises above the normal level, giving time to act before flooding. Some connect to phones.
The discharge line
Water must be discharged far enough from the house that it doesn't flow back to the foundation, and in a way that doesn't flood neighbors or violate local rules. In cold climates, discharge lines can freeze; they should be sloped to drain and may need a freeze-resistant fitting near the house so water can escape if the line ices up. Many jurisdictions prohibit connecting sump pumps to the sanitary sewer.
Testing and maintenance
- Test the pump several times a year by pouring water into the pit until the float rises and the pump runs.
- Check that the discharge carries water away.
- Clean debris from the pit and the pump inlet.
- Replace backup batteries on schedule.
- Make sure the check valve on the discharge line works, so water doesn't flow back into the pit.
Questions to ask
- What size pump do I need, and why?
- What backup system do you recommend?
- Where will the water be discharged, and will it freeze?
- Does the pit have a sealed lid? (Lids reduce humidity and radon entry.)
- What warranty covers the pump and installation?
Replacing an old pump
Sump pumps wear out, and many fail without warning. If yours is old, noisy, runs constantly or cycles on and off rapidly, have it checked before the wet season. Replacing a pump on your schedule is far better than replacing it during a storm with water rising.
Pits and lids
A sealed, airtight lid on the sump pit keeps humid air and soil gases, including radon, from entering the basement, and keeps debris and small children out of the pit.