Most basements flood because pumps are undersized, installed without backup, or left without alarms. Get the sizing right for your inflow, add real-world backup power, and give yourself early warning so small leaks never turn into a soaked slab.
Size for your inflow and head height, keep water moving during outages, add alarms that alert before the pit reaches the rim.
Safety and scope
Use a GFCI protected receptacle. Do not reach into a powered pit. Route discharge away from the foundation. Treat dirty water as a hygiene risk and wear gloves, eye protection, and a respirator if the area is musty.
How to size a pump correctly
Estimate inflow
- Catchment area in square feet times rain depth per hour times runoff coefficient times 7.48 gives gallons per hour.
- High water tables can add steady inflow even with light rain. Time your current pump cycles during a wet week.
Account for dynamic head
- Measure vertical lift from pit waterline to discharge outlet. Add losses from elbows, long runs, or small pipe.
- Pump curves drop as head rises. A unit rated 3000 GPH at 0 ft may deliver about 1800 to 2200 GPH at 10 ft.
Choose with margin
- Select capacity 1.25 to 1.5 times your peak inflow at your head height.
- If you are near the limit, add a second pump on a higher float for peak sharing.
Build the stack
- Full port check valve near the pump and a union above it for service.
- Weep hole if the manufacturer requires it to prevent air lock.
Selection quick guide
| Situation | Primary pump | Backup option | Notes |
|---|---|---|---|
| Occasional storms, short lift | 1/3 to 1/2 HP submersible, 1.5 in discharge | Battery backup with higher float | Verify curve at 8 to 10 ft head |
| Frequent storms, high inflow | 3/4 HP with strong high head curve | Second AC pump, staggered float | Prefer separate circuit if possible |
| Outages are common | Efficient 1/2 HP | AGM or lithium battery kit or generator | Test runtime against duty cycle |
| No power during events | Same as above | Water powered backup and backflow preventer | Requires city water. Check local code |
Capacity estimator
Backup power choices
| Backup type | Pros | Limits | Notes |
|---|---|---|---|
| Battery backup pump | Automatic on power loss, compact | Finite runtime, batteries age | AGM is common. Lithium is lighter if approved by the kit |
| Second AC pump | Shares peak load, covers primary failure | Needs power source | Use a higher float and a separate check valve |
| Generator | Long runtime | Manual start unless standby unit | Run outdoors only with a transfer solution |
| Water powered backup | No battery to maintain | Requires city water and may raise bill | Install a backflow preventer. Not for private wells |
Battery runtime calculator
Pipe size helper
Maintenance schedule
| Interval | Task | Details | Result |
|---|---|---|---|
| Monthly | Water test | Fill pit until cycle. Listen for smooth start and stop | Confirms operation |
| Quarterly | Clean pit and intake | Remove silt and stringy debris | Restores flow |
| Quarterly | Alarm test | Trip high float and lid pads | Alerts reach your phone |
| Twice per year | Check valve | Inspect for leaks or slam. Replace if needed | Prevents backflow |
| Annually | Battery load test | Measure voltage under load | Reliable backup |
| Before rainy season | Inspect discharge route | Confirm grade away from the house | No recycle path |
Every house is different so always check the manufacturer pump curve, local electrical and plumbing rules, and the exact inlet and discharge setup in your basement. Running a brief monthly test and logging results is the simplest way to catch problems before the next storm.
