A sump pump combo system pairs a primary AC pump with a battery-powered DC backup pump in the same pit, sharing one discharge line and one controller. The backup float sits slightly higher than the primary, so it only runs when the power drops or water comes in faster than one pump can clear.

That second pump matters more than most homeowners expect, because the storms that flood a basement are the same storms that knock out power. A primary pump with no backup is protection that fails at exactly the wrong moment.

Here is how combo systems are built, what they cost around Indianapolis, what installation involves, and how to tell whether you need one.

Key Takeaways

• A combo system is one pre-matched unit with a primary pump, a DC backup pump, a deep cycle battery, and a controller
• The backup pump runs on a 12 volt battery, so it keeps working through a power outage
• Installed cost typically runs $1,000 to $3,000 for a combo unit, more if the pit or discharge line needs work
• FEMA puts the damage from just one inch of water in a home at more than $25,000
• The battery is the part that fails first, and it needs replacing every three to five years

What Is a Sump Pump Combo System?

A combo system is a single assembly with both pumps already matched, mounted, and plumbed to work together. You are not bolting two separate products into a pit and hoping they cooperate.

Four parts make it a system rather than a pile of hardware:

• Primary pump. A standard 120V AC submersible pump doing nearly all the work in normal conditions
• Backup pump. A 12V DC pump that stays idle until it is needed
• Deep cycle battery. The power source for the backup, kept topped up by a charger on the controller
• Controller. Monitors power, battery health, and pump function, and sounds an alarm when something is wrong

How the Two Pumps Hand Off

The backup pump’s float switch is set an inch or two above the primary’s. In normal rain, the primary cycles on, clears the pit, and shuts off. The backup never moves.

Water only reaches the higher float in two situations: the primary lost power, or the primary is running but cannot keep up with the inflow. Either way, the backup starts on battery power and pushes water out through the same discharge line.

Combo Unit or Add a Backup to What You Have?

If your primary pump is only a few years old and running well, a standalone backup pump added alongside it is the more affordable path. If your primary is eight or ten years old, replacing the whole thing with a matched combo unit usually makes more sense than adding a backup to a pump that is nearly finished anyway.

Why Does a Backup Pump Matter in Central Indiana?

Indiana gets its heaviest rainfall stretches in spring, and the Indiana DNR tracks monthly precipitation against normal across all nine climate divisions. Those spring systems arrive with wind and lightning, which is when power lines come down.

So the pump stops at the same moment the water table peaks. That is not bad luck, it is the pattern.

What a Failure Actually Costs

FEMA reports that one inch of water in a home can cause more than $25,000 in damage. A finished basement with drywall, flooring, and stored belongings runs higher than that.

It is also worth knowing what your policy covers. FEMA’s own guidance explains that basement coverage under a flood policy is limited to structural items and equipment like the furnace and water heater, while contents coverage has to be bought separately. Standard homeowners policies typically exclude sump pump failure entirely unless you add a water backup rider.

It Is Not Only About Outages

Primary pumps fail on their own too. Float switches stick, impellers clog with grit, and motors burn out after seven to ten years of service. Most homeowners have no idea how old their pump is.

A Beech Grove homeowner with a finished basement had us out for a routine plumbing inspection. The original pump, around eleven years old, was running but cycling oddly. We replaced the failing primary and added a battery backup before the spring rain season. The basement stayed dry through the wettest stretch of the year, and the backup ran during a power outage that would otherwise have flooded the space.

Combo System vs Standalone Backup vs Water-Powered Backup

Three ways to get a second layer of protection, and they suit different houses.

Option	Installed cost	Best for	Watch out for
Combo unit	$1,000 to $3,000	Aging primary pump, full replacement	Higher upfront spend
Standalone battery backup	$600 to $2,000	Newer primary pump still in good shape	Pit must fit both pumps
Water-powered backup	$300 to $1,000	Long outages, city water only	Will not work on well water, uses city water while running

Water-powered backups run on municipal supply pressure, so they pump indefinitely with no battery to maintain. They need a code compliant backflow preventer on the supply line, and they are off the table if you are on a well.

What Does a Combo System Cost to Install?

The unit itself is usually the smaller part of the bill. What drives the total is the condition of the pit, the discharge line, and the outlet.

Component	Typical range
Combo unit	$350 to $900
Deep cycle battery	$130 to $300
Labor	$400 to $1,200
New sump pit if none exists	$300 to $2,500
Dedicated outlet or electrical work	$250 to $900

Most Southside installs where a working pit and discharge line already exist land in the $1,000 to $2,000 range. Homes needing a new pit cut into a concrete floor go well above that. If the number is more than you planned for this month, plumbing financing spreads it out, which beats waiting until April to find out the old pump quit.

What Does Installation Actually Involve?

A straightforward combo swap takes two to four hours. Here is the sequence:

1. Check the pit. Most codes want at least an 18 inch basin diameter for a dual pump setup. A narrow old pit sometimes has to be replaced or enlarged.
2. Pull the old pump and clean the pit. Years of silt and gravel come out with it, and that grit is often what killed the last impeller.
3. Set the combo assembly. The primary sits at the bottom, the backup mounts above it at the correct float offset.
4. Plumb the discharge. Each pump gets its own check valve so water cannot cycle back into the pit through the idle pump.
5. Mount the battery and controller. The battery goes in a sealed box on a raised platform, off the floor, where a few inches of water cannot reach it.
6. Test both pumps. Fill the pit, confirm the primary clears it, then unplug the primary and keep filling until the backup takes over on its own.

That last step is the one that gets skipped. If nobody watched the backup actually run, nobody knows it works.

How Do You Maintain a Combo System?

Combo systems are low maintenance, not no maintenance. The failure point is almost always the battery.

• Test both pumps twice a year, spring and fall, by filling the pit with a bucket
• Replace the battery every three to five years, before it fails on its own
• Check the pit for silt and gravel buildup once a year
• Confirm the discharge line outside is clear and not frozen shut in winter
• Listen for the controller alarm and do not ignore it when it sounds

If your controller is reporting a low battery in October, that is not a today problem, but it is a this-year problem. Handle it before the spring rain.

Get Your Sump Pump Checked Before Spring Rain Hits

A combo system gives you two pumps in one pit, one of them running on a battery that does not care whether the grid is up. For a finished basement in Central Indiana, that is straightforward protection against a $25,000 problem.

If your pump is past eight years, cycling oddly, or you have never seen a backup, it is worth a look. A plumbing inspection catches a failing pump in March instead of during the storm. And if water is already coming in, that is an emergency plumbing call, not something to sit on overnight.

Call Parkhurst Family Plumbing at (317) 517-9348 for straight answers on sump pump installation across Franklin Township, Beech Grove, Southport, and Greenwood. Upfront pricing, options explained before work starts, and we will tell you honestly whether a repair, a backup, or a full combo system is the right spend.