1/3 HP vs 1/2 HP sump pump
The most common sizing question in the category, and the one most often answered by buying more pump than the pit can use.
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Horsepower is a proxy for flow, and flow only means anything at a stated lift. A 1/3 HP pump and a 1/2 HP pump of the same design look much closer at zero feet than they do at twelve, because the bigger motor holds its output further up the curve. That is the whole difference, and it explains when each one is right.
What each size actually does
| Lift | 1/3 HP (typical) | 1/2 HP (typical) |
|---|---|---|
| 0 ft | Around 2,500–3,000 GPH | Around 3,000–4,000 GPH |
| 5 ft | Around 2,200–2,700 GPH | Around 2,900–3,500 GPH |
| 10 ft | Around 1,700–2,200 GPH | Around 2,400–3,000 GPH |
| 15 ft | Marginal to zero | Around 1,300–2,000 GPH |
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Zoeller 1073 (1/3 HP cast iron submersible)A third of a horsepower covers most houses, and runs longer cycles doing it. | Standard lift, standard pit | 8.9 | Check price on Amazon #ad we earn a commission · Amazon shows the current price |
| 2 |  Zoeller 1075 (1/2 HP cast iron submersible)The same pump with more behind it, for the genuinely harder pit. | High lift or fast inflow | 8.5 | Check price on Amazon #ad we earn a commission · Amazon shows the current price |
Scores are ours and editorial, not lab measurements — see how we pick. Tap a row for the full write-up.
Zoeller 1073 (1/3 HP cast iron submersible)
A third of a horsepower covers most houses, and runs longer cycles doing it.
#ad we earn a commission · Amazon shows the current price
| Type | Submersible, cast iron |
|---|---|
| Horsepower | 1/3 HP |
| Line | Zoeller at Home consumer range |
This is the size the majority of American basements need, and the one most installers fit by default. In a typical pit with a typical lift it clears water comfortably and then rests, which is exactly what you want a pump to do.
What it gets right
- Enough flow for a typical 8–10 ft lift with normal inflow
- Draws less current, which matters for backup generators
- Longer, gentler cycles in a standard pit
Where it falls short
- Marginal above about 12 ft of lift
- Struggles when the pit refills within a minute
Specifications from Zoeller at Home sump pump range.
Zoeller 1075 (1/2 HP cast iron submersible)
The same pump with more behind it, for the genuinely harder pit.
#ad we earn a commission · Amazon shows the current price
| Type | Submersible, cast iron |
|---|---|
| Horsepower | 1/2 HP |
| Line | Zoeller at Home consumer range |
Step up when the arithmetic says to, not because bigger sounds safer. The two conditions that justify it are a lift above roughly 12 feet, and a pit that refills faster than the smaller pump can clear it during a storm.
What it gets right
- Meaningfully more flow at the same lift
- Comfortable where a 1/3 HP pump is working at its limit
- Identical platform, so nothing else about the install changes
Where it falls short
- Short-cycles in a pit that does not need it
- Higher current draw to size a generator around
Specifications from Zoeller at Home sump pump range.
Work out which you need in five minutes
- Measure the vertical liftFrom the pump discharge to the highest point the water reaches in the pipe. For most basements this is 8 to 10 feet.
- Add for the horizontal runRoughly one extra foot of equivalent head for every ten feet of horizontal pipe, and a little more for each elbow.
- Time the inflowDuring steady rain, unplug the pump and time how long the water takes to rise one inch, then convert to gallons per minute using the pit area.
- CompareIf the inflow is comfortably under the smaller pump's flow at your total head, buy the 1/3 HP. If it is close or over, step up.
The full version of this calculation, including pit area tables, is in what size sump pump do I need.
Questions people ask
Is 1/3 HP enough for a basement sump pump?
For most basements with up to about 10 feet of lift and normal inflow, yes. It is the most commonly installed size in the country for good reason.
When should I upgrade to 1/2 HP?
When the lift exceeds roughly 12 feet, when the horizontal run is long, or when the pit refills faster than the current pump can clear it during sustained rain.
Does a bigger pump use much more electricity?
Per hour of running, yes, but a bigger pump also runs for less time to move the same water. The practical difference on a utility bill is small; the difference that matters is generator sizing during an outage.
Can I put a 1/2 HP pump in a small pit?
You can, and it will short-cycle. If the pit is small and the inflow is high, widening or deepening the pit is a better answer than adding horsepower.
Sources
Read next
What size sump pump do I need?
Two measurements and ten minutes give you a real answer. Almost everyone skips both and buys on horsepower instead.
1/2 HP vs 3/4 HP sump pump
Past half a horsepower, the pump usually stops being the limiting factor. Here is how to tell whether you are in the small group that genuinely needs more.
The best sump pumps, ranked by what they move at real lift
Five pumps that cover almost every residential pit, compared on the number that matters: how much water they move at the height your basement actually needs.
Sump pump horsepower, explained
Horsepower is a proxy for flow, and flow only means anything at a stated height. Here is how to read the numbers on the box.
What size should a sump pit be?
The hole constrains everything that goes in it. Pit dimensions rule out more pumps than horsepower ever will.