Sump pumps are sold on horsepower and on a gallons-per-hour figure. Neither describes what the pump will deliver in your basement.
Total head is the real input
Head is the work the pump does against gravity and friction:
Vertical lift — from the water level in the basin to the discharge point, typically 8 to 12 feet in a residential basement.
Friction loss in the horizontal run, the elbows and the check valve, which is added as equivalent feet.
Discharge height above grade at the far end.
Total head of 10 feet is common; 15 or more is not unusual with a long run.
Read the pump curve, not the headline
Every manufacturer publishes a performance curve — flow at each head height. That is the number that matters.
A pump advertised at 3,000 gallons per hour may deliver 2,000 at 10 feet of head and 1,200 at 20. The advertised figure is measured at zero lift, which no installation has.
Find your total head, read the curve at that point, and compare pumps on that number.
How much capacity you need
Measure it. With the pump disconnected during wet weather, time how long the basin takes to fill a known depth. That gives the inflow rate directly.
For most residential basements, a third to a half horsepower is adequate once head is accounted for. A larger pump does not help if the inflow is modest — it short-cycles, which wears the switch and the motor.
Bigger is not better. Correctly sized is.
Switch type is where pumps actually fail
The motor rarely fails first. The switch does.
Tethered float — a float on a cord. Simple, reliable, needs a wide basin so it does not hang up on the wall or the pipe.
Vertical float — moves up a rod. Works in a narrow basin, shorter travel so it cycles more often.
Electronic — no moving float. No mechanical wear, and dependent on electronics in a wet environment.
Whatever the type, the failure mode to guard against is the float catching on something. Keep the basin clear and check the float travel when testing.
Backup is not optional
Pumps fail during storms, and storms cause power cuts. A primary pump with no backup is a system that is offline at the exact moment it is needed.
Battery backup — a second pump on a deep-cycle battery, sized for hours of runtime. The standard answer.
Water-powered backup — driven by mains water pressure, no battery to maintain, uses a lot of water while running, and prohibited in some jurisdictions.
A generator covers the primary pump and everything else, and requires someone to be home to start it unless it is a standby unit.
The check valve and the discharge
A check valve stops the column of water in the discharge pipe running back into the basin when the pump stops. Without it, the pump re-pumps the same water and cycles constantly.
The discharge must reach well away from the foundation, and it must not freeze. A frozen line means the pump runs against a blockage.
Many installations use a freeze-relief fitting near the house so that if the line ices up, water escapes there rather than backing up.
Maintenance, twice a year
Fill the basin with a bucket and confirm the pump starts, runs and stops. Do the same for the backup with the primary unplugged.
Clear debris from the basin. Check the check valve for leaks. Walk the discharge line to its outlet.
Ten minutes, twice a year, on the one component the whole system depends on.