The best combination sump pump systems
One box, two pumps, floats already set at the right heights. It removes the mistake that disables most home-built backup installations.
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A combination system is a primary pump and a battery backup sold as one matched assembly: one lid, two pumps, one controller, and float heights already set relative to each other. The components are not individually better than buying separately. What you are paying for is that the system is correct out of the box.
When a combination system is the right buy
- Your primary pump is at or near end of life. If you are replacing it anyway, the incremental cost of the backup half is modest.
- You are installing a pit from scratch. Everything is sized together and the plumbing is supplied.
- You want the install to be right without becoming an expert in float heights. This is a real and sufficient reason.
When to buy the two halves separately
- Your primary is new. Do not discard a healthy pump to buy a bundle.
- You want specific components. A Liberty primary with a Wayne backup is a perfectly sensible pairing that no bundle offers.
- Your pit is tight. A separate low-profile backup may fit where a matched pair does not.
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Basement Watchdog Big ComboA 1/2 HP cast-iron primary, a 12 V backup, dual floats on both, and the plumbing bits in the box. | A complete replacement | 9.0 | Check price on Amazon #ad we earn a commission · Amazon shows the current price |
| 2 |  Zoeller AquaNot 508 battery backup systemThe self-testing route for anyone whose primary pump is still healthy. | Adding a backup to a good primary | 8.6 | Check price on Amazon #ad we earn a commission · Amazon shows the current price |
| 3 |  Wayne ESP25N battery backup systemThe backup to choose when you want the two pumps to be closer to each other in capacity. | Pairing with a high-flow primary | 8.3 | 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.
Basement Watchdog Big Combo
A 1/2 HP cast-iron primary, a 12 V backup, dual floats on both, and the plumbing bits in the box.
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| Type | Pre-assembled primary + 12 V DC backup combination |
|---|---|
| Primary pump | 1/2 HP cast iron |
| Switch | Dual float switches on both the primary and the backup |
| Included | Primary pump, 12 V backup pump, primary controller, Wi-Fi capable backup controller, two dual float switches, 1.6 A charger, two check valves, 1-1/2 in rubber union, battery box |
| Battery | Not included, sold separately |
| Flow, by lift | 4,400 GPH at 0 ft · 2,600 GPH at 0 ft |
The real argument for a combination system is not price, it is correctness. A home-assembled primary-plus-backup is only as good as the relative float heights, and getting those wrong — backup set too low — is the single most common reason a backup system fails to help.
This one arrives with that worked out, with two check valves so the backup is not pushing water through a dead primary, and with dual floats on each pump so a single stuck switch does not take anything offline.
What it gets right
- Dual float switches on BOTH pumps, which is four chances for the system to notice water
- Two check valves and the rubber union supplied, so the discharge is done properly
- Wi-Fi capable backup controller for remote alerts
Where it falls short
- Battery sold separately
- Needs a pit large enough for two pumps and their floats to work independently
- Both halves come from the same manufacturer, for better and worse
Specifications from Basement Watchdog Big Combo specification listing.
Zoeller AquaNot 508 battery backup system
The self-testing route for anyone whose primary pump is still healthy.
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| Type | 12 V DC battery backup pump, self-testing |
|---|---|
| Monitoring | Alerts on power outage, high water and switch obstruction |
| Run time | Up to about 6 hours of continuous pumping |
| Battery | 12 V deep-cycle, sold separately on most SKUs |
| Flow, by lift | 2,340 GPH at 5 ft · 1,800 GPH at 10 ft |
| Warranty | Three years, limited |
Zoeller sells this both as a standalone backup and bundled with an M53 primary, which makes it the flexible answer. If your primary is a healthy cast-iron pump with years left, adding this beside it is better value than replacing the lot.
What it gets right
- Self-tests rather than waiting for a real outage to reveal a fault
- Available bundled with an M53 primary if you do want both at once
- Three-year limited warranty
Where it falls short
- Battery sold separately
- Lower backup flow than the Wayne system
Specifications from Zoeller AquaNot 508 battery backup listing, Zoeller 508-0006 AquaNot with M53 primary.
Wayne ESP25N battery backup system
The backup to choose when you want the two pumps to be closer to each other in capacity.
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| Type | 12 V DC battery backup pump |
|---|---|
| Housing | Epoxy-coated steel with a cast-iron base |
| Impeller | Corrosion-resistant thermoplastic |
| Discharge | 1-1/2" NPT |
| Battery | One Group 27 deep-cycle battery, sold separately |
| Minimum basin | 14 in diameter |
| Monitoring | LED display and audible alarm on the battery case |
| Flow, by lift | 2,900 GPH at 0 ft · 2,340 GPH at 5 ft · 1,680 GPH at 10 ft · 600 GPH at 15 ft |
| Warranty | Two years |
Pairing this with a 1/2 HP primary gets you closer to true redundancy than most combinations, because the backup is not dramatically weaker than the pump it is covering for.
What it gets right
- 1,680 GPH at 10 ft is the strongest backup flow here
- Steel and cast-iron construction
- Fits a 14-inch basin, so it squeezes in beside an existing pump
Where it falls short
- Single float
- Battery separate
- Flow drops hard above 10 feet
Specifications from Wayne ESP25N specification listing, Wayne ESP25 product listing.
Getting the float heights right
Whichever route you take, this is the detail that determines whether the system helps. The backup's switch-on level must sit ABOVE the primary's, with enough separation that normal cycling never reaches it. The backup should only ever start when the primary has failed, has lost power, or genuinely cannot keep up.
Set them too close and the backup joins in on ordinary cycles, running the battery down over weeks until the night it is needed. Set them too far apart and water rises uncomfortably high before the backup wakes up. A separation of a few inches, with the backup's intake still well below the floor slab, is the target.
Questions people ask
Is a combination sump pump worth it?
If you are replacing the primary pump anyway, usually yes: the backup half costs less bundled than bought separately, and the float heights and check valves arrive correct.
Can I add a backup to my existing sump pump?
Yes, and it is the right move if the primary is healthy. You will need room in the pit, a second check valve, and the backup float set above the primary's switch-on level.
Do combination systems need a bigger pit?
Generally yes. Two pumps and up to four floats need room to operate without touching each other or the basin wall. An 18 by 22 inch basin is the practical minimum and larger is better.
Does the backup pump use the same discharge pipe?
It can, provided each pump has its own check valve before the two lines join. Some installers run a separate discharge for the backup, which is more work but removes a shared point of failure.
Sources
Read next
The best battery backup sump pumps
The storm that fills your pit is the storm that takes the power out. This is the half of the system that works when the other half cannot.
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.
The best sump pump check valves
A forty-dollar valve is the single most common reason a healthy pump appears to be failing. It is also the easiest thing in the pit to replace.
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.
The best batteries for a backup sump pump
Your backup system is only as good as the battery behind it, and the battery is the part everyone forgets until the night it matters.