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Sump & Seal

Sump pumps, chosen by lift and pit size — not by horsepower on the box

The pump that keeps a basement dry is rarely the biggest one. It is the one sized to how high it has to push water and how fast the pit refills.

Almost every sump pump listing leads with two numbers: horsepower, and a gallons-per-hour figure measured at zero feet of lift. Neither of those is the number that matters in your basement. A pump in a typical home has to lift water eight to ten feet to get out of the pit and up to the rim joist, then push it through twenty or thirty feet of pipe to daylight. At that lift, a pump advertised at 4,000 GPH may be moving closer to 2,000.

So the first thing we do on every pump page is quote flow with the lift it was measured at. The content model on this site makes that literally unavoidable — a flow figure cannot be stored without its lift — because quoting the zero-foot number as real-world performance is the single most misleading convention in this category, and several large publishers still do it.

Start with what size sump pump you need if you are replacing one and do not know what you had. If you already know the size and just want the shortlist, the best sump pumps roundup is the fastest route to a decision.

A submersible sump pump sitting in a concrete sump pit

In this section

How to choose a sump pump

Four decisions cover almost every basement. Make them in this order, because each one narrows the next.

1. Measure the lift before you look at horsepower

Total dynamic head is the vertical distance from the pump's discharge to the highest point in the pipe, plus friction losses along the run. For most houses that lands between 8 and 12 feet. A 1/3 HP cast-iron pump moves roughly 2,000-2,600 GPH at 10 feet; a 1/2 HP moves roughly 2,700-3,400. If your pit refills faster than that during a storm, you need more pump — or, more often, you need to find out why so much water is arriving.

2. Match the pump to the pit, not the other way round

A submersible pump needs a pit wide enough that the float can swing without touching the wall, and deep enough that the pump is not short-cycling on four inches of water. An 18 x 22 inch basin is the common floor. In a narrow or shallow pit, a pedestal pump with the motor above the water is often the only thing that fits — see pedestal vs submersible.

A sump pit with a submersible pump and discharge pipe installed
Pit width decides float type before horsepower decides anything.

3. Decide how much of the pump is cast iron

A cast-iron housing sinks motor heat into the surrounding water, which matters during the kind of multi-hour run that kills thermoplastic pumps. Cast iron costs more and weighs more. For a pump that runs a few times a week, thermoplastic is honestly fine. For a pit that runs every few minutes during a thaw, it is not: see cast iron vs plastic.

4. Look at the switch, because that is what fails

Motors rarely die first. Switches do. A tethered float needs swing room, a vertical float needs vertical clearance, and a solid-state switch has no moving part at all. On a pump you intend to keep for a decade, the switch type is a more consequential decision than the last 1/6 of a horsepower — and it is also the part you can replace on its own, which is covered in float switches.

What we do not do here

We have not torn these pumps down or run them on a test bench, and we do not claim to have. Every specification on this site is traced to the manufacturer's published documentation or a retail listing and linked at the bottom of the page. Where sources disagree, or where we could not find a figure, the figure is left out rather than estimated. That is the whole method, and it is written up in how we pick.

Questions people ask

Is a 1/2 HP sump pump always better than a 1/3 HP?

No. A 1/2 HP pump moves more water at the same lift, but in a pit that only collects a modest amount it will short-cycle, which wears the switch and the motor faster than steady running does. Size to the water arriving and the lift required, not to the biggest number available.

How do I know how much water my pit takes?

During steady rain, let the pit fill to the switch-on point, unplug the pump, and time how long it takes to rise one inch. Multiply by the pit's area to get a rough inflow rate in gallons per minute, then compare that with a candidate pump's flow at your lift.

Can I reuse the old discharge pipe and check valve?

Reuse the pipe if it is sound and correctly sized, but replace the check valve. A check valve is cheap, it is the part that lets water fall back into the pit when it fails, and a tired one makes a brand-new pump look faulty.

Do I need a backup pump as well?

If your basement is finished, or if a flood would reach anything you cannot replace, yes. Power outages and storms arrive together, and a primary pump with no power is just a heavy object in a hole. See the backup systems section.

Sources