The best 1/3 HP sump pumps

Zoeller M53 Mighty-Mate

The pump in this class that publishes a flow figure at ten feet of lift, inside a cast-iron housing with an oil-filled motor and a three-year warranty.

9.1/10★★★★★Our editorial score: 9.1 out of 10

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Specifications, as published by Zoeller

Type	Submersible, cast iron
Horsepower	3/10 HP (sold as 1/3 HP)
Electrical	115 V, 9.7 A, 60 Hz
Discharge	1-1/2" NPT vertical female
Switch	Integral vertical float, on at 7-1/4", off at 3"
Solids handling	1/2"
Shut-off head	19.25 ft
Flow, by lift	2,580 GPH at 0 ft · 2,040 GPH at 10 ft
Warranty	Three years

This pump wins on a single piece of honesty: Zoeller publishes what it does at ten feet of lift. The specification sheet gives 43 GPM maximum and 34 GPM at ten feet of head — about 2,580 and 2,040 gallons per hour. Almost every competitor in this class publishes the zero-lift number and stops, which means you can compare the M53 against your own measured lift and you cannot do that with most of the pumps sitting beside it on the shelf.

The hardware backs the paperwork up. The housing is cast iron, which sinks motor heat into the surrounding water during the sort of multi-hour run that a thaw or a three-day storm produces. The motor is oil-filled rather than air-cooled. The impeller is a vortex design that throws solids through rather than chopping at them, which is why the solids rating is half an inch while two of the thermoplastic pumps below are rated at three eighths.

Be clear about what you are not buying. The M53 is the entry model of that family, and the base and impeller are engineered plastic — the all-cast-iron equivalents are on the M63, which also carries a longer warranty. And the 19.25 foot shut-off head is genuinely modest: plenty for a pit floor to rim-joist run in an ordinary house, and not enough for a deep basement discharging to a high grade. Measure first; the arithmetic is in what size sump pump do I need.

One practical note that costs people money: the 9.7 A draw matters on a shared circuit. If the sump outlet also carries a freezer or a dehumidifier, that combination is how a pump ends up behind a tripped breaker during the one storm it needed to run through. Read sump pump tripping breaker before you reuse an old outlet.

Specifications from Zoeller M53 (53-0001) specification sheet.

Wayne CDU790

3,060 GPH published at ten feet of lift — half again the M53 at the same height — from an epoxy-coated cast-iron body with a top-suction intake.

8.9/10★★★★★Our editorial score: 8.9 out of 10

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Specifications, as published by Wayne Water Systems

Type	Submersible, epoxy-coated cast iron
Horsepower	1/3 HP
Electrical	120 V, 9.5 A, PSC oil-filled motor
Discharge	1-1/2" NPT
Cord	8 ft
Switch	Vertical float
Flow, by lift	4,600 GPH at 0 ft · 3,060 GPH at 10 ft
Warranty	Three years (the CDU790SS stainless variant is five)

If you want the most water moved at the lift a normal basement actually imposes, this is the pump. 3,060 GPH at ten feet is roughly fifty percent more than the M53 manages at the same height, out of a motor drawing almost exactly the same current. That is not marketing; it is a published pair of figures at a stated lift, which is the only kind of flow number we will rank on.

The top-suction intake deserves a sentence of its own. Most submersibles draw from a screen around the base, inches from whatever has settled on the pit floor. Wayne moves the intake up the body, which means the pump is pulling from cleaner water and the impeller sees less grit over a decade. In a pit that silts up — and most pits fed by drain tile do — that is a longevity feature rather than a spec-sheet one.

Two constraints will decide this for you before the flow curve does. The pump wants an 11 inch or larger pit, and the cord is eight feet. Measure the basin and the distance to the outlet, in that order. If either number is tight, the pump below is the one that fits.

Specifications from Wayne CDU790 specification listing, Wayne CDU790 distributor listing.

Liberty Pumps 257

A one-piece cast-iron pump rated to run in a 10 inch pit, with 23 feet of maximum head and a magnetic float on a quick-change 10 ft cord.

8.6/10★★★★★Our editorial score: 8.6 out of 10

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Specifications, as published by Liberty Pumps

Type	Submersible, Class 25 cast iron
Horsepower	1/3 HP
Electrical	115 V, 5.2 A
Discharge	1-1/2" NPT vertical female
Impeller	Thermoplastic vortex
Solids handling	3/8"
Minimum pit	10 in diameter
Maximum head	23 ft (rated head 5 ft)
Flow, by lift	2,640 GPH at 0 ft
Warranty	Three years

This is the pump you buy when the pit is the problem. A 10 inch rating is unusual — most submersibles in this class need eleven inches or more just for the float to clear the wall — and narrow pits are common in older houses, in crawl spaces, and wherever a pit was cut in after the slab was poured. If a tape measure across your basin reads under eleven inches, the shortlist is this pump and a pedestal.

The casting is the second argument. Liberty pours the motor housing and the volute as a single piece of Class 25 cast iron, so there is no bolted joint and no gasket between them. On a pump expected to sit in water for ten years, removing a seam is worth more than most of the features printed on the box. The vertical magnetic float is the same philosophy applied to the part that actually breaks: no arm, no pivot, and a cord that disconnects so the switch can be changed without unplumbing the pump.

The honest weakness is data. Liberty gives a zero-lift flow and a maximum head and nothing in between, so we cannot tell you what this pump does at ten feet, and we are not going to interpolate a curve and present it as a specification. It ranks third on published performance and it would rank first on pit fit, which is exactly how you should read it.

Specifications from Liberty 257 specification listing, Liberty 250-series distributor spec page.

Superior Pump 92341

2,760 GPH at zero lift, 25 feet of maximum head and a stainless impeller inside a cast-iron body, for well under what the name brands charge.

8.2/10★★★★★Our editorial score: 8.2 out of 10

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Specifications, as published by Superior Pump

Type	Submersible, cast iron
Horsepower	1/3 HP
Electrical	120 V, 4.1 A
Discharge	1-1/2"
Switch	Vertical float
Motor	Continuous duty, thermally protected split capacitor
Flow, by lift	2,760 GPH at 0 ft
Warranty	Three years

There is a real pump under the price here. Cast iron, a stainless impeller, a split-capacitor motor with thermal protection, and the highest published maximum head in the group at 25 feet. For a basement with a modest pit and an ordinary number of cycles a week, this does the same job as a pump costing substantially more, and the 4.1 A draw is the lowest on this page by a distance.

What you give up is partly data and partly depth. There is no gallons-at-ten-feet figure, so the 25 foot head number has to carry the sizing decision on its own. And the specification sheet stops at the headline items — nothing about bearings, nothing about the seal stack — which are exactly the components that separate a pump that lasts four years from one that lasts twelve.

Buy this if the pit is undemanding, or if it is the second pump in the pit. In a two-pump arrangement, spending the money on the primary and putting a cheaper cast-iron pump on the higher float is a perfectly rational split — see two sump pumps in one pit.

Specifications from Superior Pump 92341 specification listing.

Zoeller 1073 (1/3 HP cast iron submersible)

The cast-iron 1/3 HP pump from Zoeller's consumer range: the right name and the right housing, with almost nothing published to size it by.

7.6/10★★★★★Our editorial score: 7.6 out of 10

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Specifications, as published by Zoeller

Type	Submersible, cast iron
Horsepower	1/3 HP
Line	Zoeller at Home consumer range

Zoeller runs two ranges: the professional line the plumbing trade buys, where the M53 lives, and the Zoeller at Home consumer range, where the 1073 lives. The 1073 is a cast-iron 1/3 HP submersible and it is a sound pump in the way that any cast-iron Zoeller is a sound pump.

It ranks fifth here for one reason, and it is not build quality. The consumer-range listing gives horsepower and housing material and essentially nothing else — no flow at any lift, no amps, no float trip points — and we will not fill those cells in from a sibling model and present the result as a specification. If the retail shelf is your constraint, buy it without worrying. If you can order a pump, the M53 is the same company being far more forthcoming.

Specifications from Zoeller at Home sump pump range.

Superior Pump 92330

The cheapest honest way to have a working 1/3 HP pump in the house, with a thermoplastic body and a tethered float that both come with conditions.

7.2/10★★★★★Our editorial score: 7.2 out of 10

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Specifications, as published by Superior Pump

Type	Submersible, thermoplastic
Horsepower	1/3 HP
Switch	Tethered float
Flow, by lift	2,400 GPH at 0 ft

Every sump pump page should have one entry that is honest about being the cheap option. This is it: 2,400 GPH at zero lift, a thermoplastic body, a tethered float, and a price that makes it reasonable to own one you are not currently using.

The material is the real trade. Cast iron conducts motor heat away into the water around it; plastic does not, which is why thermoplastic pumps are the ones that die during the storm where the pit ran continuously for six hours. The tethered float is a smaller trade with a genuine upside: it switches off lower in the pit than a vertical float does, so the pump runs longer and starts less often — in a pit wide enough to let the float swing. In a narrow pit it is simply the wrong switch, and the comparison is in vertical vs tethered float switch.

Specifications from Superior Pump brand listing.