sump pump · guide · TN LLP #5045

What Size Sump Pump Do I Need?

Sizing to how fast the pit actually fills, not to the horsepower on the old one.

Short answer

Size to how fast the pit refills with the pump switched off, plus the height the water has to be lifted and the length of the run to the outlet. Not to the horsepower stamped on the old pump. Oversizing is a real failure mode here, not a safe default.

The usual way people choose a replacement sump pump is to read the horsepower off the one that died. That number tells you what somebody bought once. It does not tell you what the house needs, and if the old pump was wrong, matching it repeats the mistake.

The number that actually matters

It is the fill rate: how fast water comes back into the pit when the pump is off. That is measurable in a few minutes at the house, and it is the only figure that describes your ground rather than somebody else's.

Then two more: the vertical lift from the pit to the discharge, and the length of the horizontal run after that. Both cost the pump capacity. A pump rated comfortably above your fill rate on paper can still fall behind once it is lifting eight feet and pushing forty across a crawlspace.

Why bigger is not safer

A pump that empties the pit much faster than the pit fills will start, run for a few seconds, stop, and start again. Every start is the hardest moment in a motor's life, and short-cycling is one of the main things that kills sump pumps early.

So oversizing does not buy you insurance. It buys you a pump that wears out faster and is more likely to be dead when the storm you bought it for finally arrives.

Crawlspace pits are not basement pits

Almost all the sizing advice online assumes a full basement: a deep pit, a short lift, a discharge through a nearby wall. Across this corridor the house is usually on a crawlspace, the pit is shallower, and the run to somewhere the water can actually leave is longer.

A shallower pit means less water stored between cycles, which pushes you toward a smaller pump, not a bigger one, if you want to avoid short-cycling. That is the opposite of what most of the internet will tell you.

What we would do

Do not size off the old label. Let us time the fill rate and measure the lift and the run, then size to that. It usually lands on a smaller pump than people expect, and it lasts longer.

Permits

Some plumbing work requires a permit and an inspection, and some does not. Whether one is required for your job is determined by the Authority Having Jurisdiction — the city or county building and codes office for your address — and it is at their discretion.

Usually requires a permit

Water heater replacement and tankless conversion
Whole-house repiping
Water service line and sewer line replacement
Gas line installation and repair
Relocating a fixture to a new position

Usually does not

Drain cleaning and clearing blockages
Emergency and repair work
Like-for-like fixture replacement
Water heater repair
Camera inspection and diagnostics

This is general guidance rather than a ruling, and it can differ from one town to the next. The Authority Having Jurisdiction makes the determination. Across the Bradley–McMinn corridor we pull the permit and book the inspection ourselves. Inside Hamilton County and Chattanooga the permit office does not accept an application from our license class, so permit-required jobs there are referred to a licensed partner who does the work and meets the inspector.

Common questions

What Size Sump Pump Do I Need — questions

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

Not inherently. Better means matched to your fill rate, lift, and run. A 1/2 HP pump in a shallow crawlspace pit that fills slowly will short-cycle itself to death while a 1/3 HP one runs quietly for years.

How do you measure the fill rate?

Switch the pump off, mark the level, and time how long the pit takes to rise a known amount. It takes a few minutes and it is a real number about your house rather than a regional average.

Does the discharge length really change the pump I need?

Yes. Every foot of lift and every foot of horizontal run costs flow. Two identical pumps in two houses deliver different real-world capacity because of it, and crawlspace runs here are often long.

Do you handle the electrical side of a sump pump?

No. We fit the pump, the check valve, and the discharge line. The dedicated circuit and the receptacle are an electrician’s license, not a plumber’s. We will tell you when the fault or the requirement sits on that side so you are calling the right trade.

Will I know the price before you start?

Yes. One number to approve before the work begins, and it holds. This market has a documented habit of quotes climbing mid-job; we built the opposite habit deliberately.

Are you licensed?

Yes. Tennessee Limited Licensed Plumber #5045, verifiable at verify.tn.gov. Across eighteen local competitors, not one publishes their number.

Book Drain Pros TN for sump pump replacement.

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