Sump pump battery backup, water-powered pumps and alarms

1. Main pump
2. Backup pump on a block, with its float set higher
3. High-water alarm sensor
4. Alarm unit with its own battery and phone notification
5. Battery for the backup pump
6. A separate discharge and check valve for each pump

Do you need a backup or just an alarm?

For me, if a basement depends on the sump pump to keep from flooding, it needs a backup. Especially when:

• the basement is finished;
• the pump works hard when it rains;
• groundwater rises quickly;
• the power goes out in your area;
• the owners travel;
• a flood would cause serious damage.

An alarm alone may be enough in a house where the pump rarely runs and someone can react quickly.

I explain the difference with a simple example. If the pit can overflow in twenty minutes and you’re two hours from home, a notification on your phone isn’t a backup. A backup can keep the pit under control while you find out why the main pump stopped. One gives you information; the other gives you time.

Sump pump battery backup

A battery backup is usually a second pump that runs on a battery. It has its own float or controller and turns on when the main pump fails, when the power goes out, or when the water rises above the normal level.

How long it lasts has no fixed number. It depends on the battery, its age and charge, the pump, the lift height and above all how much water is coming in. I think of it in hours, not days. As a planning range, I use six to twelve hours of hard running for some systems, and that’s a range from experience, not a specification or a guarantee. If the pump only runs now and then, the battery can last much longer.

Maintenance:

• check the charger or controller;
• test it regularly;
• keep the terminals clean;
• check the electrolyte if the battery needs it;
• replace the battery according to its condition and the manufacturer’s guidance.

I start to distrust many backup batteries at around three to five years. That’s my field criterion, not a rule.

Water-powered backup sump pumps

A water-powered backup doesn’t need electricity or a battery. It uses the pressure of the city water supply to create suction and pull water out of the pit, so it keeps working during an outage as long as the water supply holds. It needs enough water pressure and flow, properly sized plumbing and backflow protection. As an example, one manufacturer’s installation instructions call for at least 40 PSI of water pressure and a listed backflow prevention device installed according to local code, and the amount of water the pump moves depends on that pressure.

It isn’t a backup for a home on a private well: when the power goes out, the well pump usually stops too. It also uses drinking water to remove groundwater, so it isn’t my first choice in every house. Because it connects to the drinking water supply, I leave the connection to a plumber and to local code.

A second pump or a generator

A second electric pump can work well where a lot of water comes in. I set its float a little higher than the main pump’s, so the two don’t run all the time. It has to be truly independent: if it shares the same outlet, the same circuit or the same discharge, it fails for the same reasons as the first one.

A generator can keep the main pump running during a long outage, especially if it also has to power other things in the house. A portable generator has to run outside, never in the basement, the garage or next to doors, windows or vents. It should never be connected to the electrical panel with an improvised setup.

For a high-risk house, I don’t think it’s excessive to have a main pump, an independent backup and an alarm, plus a generator where long outages are common.

Sump pump alarms

The minimum is a high-water alarm in the sump. Its sensor goes above the level where the main pump normally starts and below the level where the pit would overflow, so it warns you when something isn’t working as it should.

I also like leak sensors:

• around the pit;
• by the water heater;
• by mechanical equipment;
• at the low points of the basement.

If the owners travel, I prefer alarms that can send a notification to a phone, because a siren in the basement doesn’t help if nobody is home. The alarm should have its own power source or a battery, since an alarm that dies in the same outage as the pump isn’t much help. And you should test it.

Backup options compared

FEMA’s guide on basement flooding also lists a battery-powered backup pump among its mitigation measures. Test the backup and the alarm separately when you test the sump pump, three or four times a year in my routine.