A sump pump only does its job as long as it has power. That sounds obvious until the exact moment it matters, a storm heavy enough to flood the yard and take down the line at the same time. In the Upstate that is a summer thunderstorm that floods a crawl space in an hour, or an ice storm that takes the power for days. This post follows one storm night under a Greenville home three times: with a sump pump alone, with a pump and a battery backup, and with a pump and a standby generator. The water level makes the argument.
A summer storm on saturated clay
It is a July evening after a wet week. The red clay under the house is already holding water, a thunderstorm drops two inches of rain in an hour, and at 9:40 a limb comes down on a line two streets over. The power is out, the utility’s estimate is morning, and water is entering the sump pit faster than it has all year. Here is what happens next in three versions of the same house.
With the sump pump alone
A standard sump pump runs on household electricity and has no way to keep working once that power is gone, so at 9:40 it stops. Water keeps rising in the pit the entire time the power is out, and a hard Upstate rain pushes plenty of it into that pit in a short time. By midnight the pit has overflowed, by the time the power returns at 6:00 the crawl space is standing in several inches of water, and the household discovers it days later as a musty smell upstairs. Flooding under a house most often happens overnight or while the family is away, which is why nobody was there to notice. What follows is wet insulation, wet ductwork that pushes mold into the house every time the air conditioner runs, and sometimes a joist that has to dry for weeks.
With a battery backup
In the second version, the pump has a battery backup, a second pump or a battery-driven controller that takes over when the power drops. At 9:40 the backup pump starts, and the pit stays at its normal level. The battery runs the pump for several hours, depending on how hard it has to work, and on this night, with the power back at 6:00, it carries the crawl space through and recharges the next day. That is a good outcome, and a battery backup is worth installing on any Upstate sump pump for exactly this kind of night, but its limit is the length of the outage. A battery that covers a summer thunderstorm’s eight hours does not cover the ice storm that keeps the power down for three days while the melt keeps filling the pit, and it does not cover the well pump, the heat, or the refrigerator.
With a standby generator
In the third version, the house has a whole-home generator wired through an automatic transfer switch. At 9:40 the power drops, and within about ten to thirty seconds the generator has started on its own and the transfer switch has handed the house to it, so the sump pump never noticed. It runs through the night as it would on any other night, along with the air conditioning, the refrigerator, the well pump if the home has one, and the lights, and it keeps running whether the outage lasts until morning or, as in the ice storms of 2005 and 2014 and the week after Helene in 2024, for days. Nobody has to be home or awake. It runs on natural gas or propane, so there is no gasoline to find, and when the utility returns, the switch hands the house back and the generator shuts itself down.
What the three versions show
The pump is the same in all three, and so is the storm. What differs is how long the pit can rise before something pumps it, and for how many hours. A pump alone protects the house on every night except the one it was installed for. A battery backup protects it through a short outage, which covers most Upstate thunderstorms, and it is the right first step for any home with a sump pump. A generator protects it through any outage, and everything else in the house with it. Homeowners who install both find the pairing useful, since the battery bridges the seconds before the generator starts and covers the pump if the generator ever needs service.
Sizing the generator for the pump
A sump pump is a motor, and motors draw a surge of current when they start, several times their running draw. A generator sized only for the running load will stall or trip when the pump kicks on in the middle of the night, so the pump’s starting current is part of the sizing along with the heat pump, the well pump, and whatever else the household wants carried. Carolina Heating Service sizes a whole-home generator from the equipment nameplates rather than square footage, and because we install and service sump pumps as well, the pump, the battery backup, and the generator can be planned as one system.
Planning for the night before it arrives
Carolina Heating Service has served Greenville and the Upstate since 1981. If your home has a sump pump and no backup power, the useful next step is a visit in which a technician looks at the pump, the pit, and the house’s outage history and lays out the battery, generator, or both options with a firm price before anything is scheduled, and financing is available for a generator. Schedule online or through the 24/7 website chat, and one call will handle the pump and the power that keeps it running.