backup
Fridge, sump, furnace: the minimum backup kit
The three loads that spoil food, flood the basement, or freeze the pipes, how many watts they actually want, and the kit that covers them without pretending you bought whole-house backup.
The lights go out and you still have three jobs. The fridge has about four hours before USDA says the perishable food is a toss. The sump is the pump that only matters in the storm that also killed the power. The furnace is gas heat that still needs a blower and an inducer, so a dark house in January is a cold house even when the gas is on. That list is the minimum kit. Everything else (the well, the medical device, the whole air conditioner) is a bigger machine, and those pages already exist.
This is not what belongs on a critical-load panel written again. That page is the circuit list and the electrician’s quote. Stay here when you are buying the first layer: a thermometer, a sump that still pumps, a way to keep the gas furnace’s electronics alive, and a small inverter or suitcase battery that can start the fridge without backfeeding the street.
Amazon links below use our Associates ID. As an Amazon Associate I earn from qualifying purchases.
What fails first, in hours?
Fridge. FoodSafety.gov, citing USDA, says a closed refrigerator keeps food safe for about four hours. A full freezer holds about 48 hours, a half-full freezer about 24 hours, if you leave the door shut. Perishable food that sits above 40°F for more than two hours on their chart is a discard, not a sniff test. An appliance thermometer is how you know. Guessing from “it still felt cold” is how you eat the leftovers anyway.
FoodSafety.gov: food safety during a power outage
A modern fridge does not draw its EnergyGuide kWh as a steady load. ENERGY STAR certified refrigerators run about 9 percent under the federal minimum, and DOE still points you at the yellow label on your door for yearly kWh. A typical full-size compressor is on the order of 100 to 250 watts while it runs, with a short start spike on older fixed-speed machines. The 24-hour average is much lower because the compressor cycles. For generator math you care about the start, then the running watts, not the yearly bill.
DOE: purchasing and maintaining refrigerators
Sump. The AC pump in the pit dies with the grid. Zoeller’s common 3/10 horsepower M53, the Mighty-Mate a lot of basements already have, is 115 volts and 9.7 amps on the spec sheet. That is about 1,115 watts while it is pumping, plus a nastier start. It does not run all night. It runs when the pit fills. A battery backup is a second pump and a battery in that pit so the storm and the outage can happen together.
HomeGuide’s 2026 battery-backup sump page is $600 to $2,000+ installed. Angi puts professional backup-battery work at $600 to $1,200, $900 average, with a published spread of $300 to $1,800. Water-powered backups (HomeGuide $300 to $1,000) need municipal water pressure and do nothing on a well.
HomeGuide: sump pump battery backup cost
Angi: sump pump battery backup cost
That backup lives in the pit. It is not an extension cord from a generator in the driveway, because the pit is in a wet hole and GFCI plus a listed backup is the job a plumber actually finishes.
Furnace. Gas still needs electricity. The burner is gas. The inducer, hot-surface igniter, control board, and blower are watts. Read the furnace nameplate in the burner compartment: volts and amps, then watts = volts × amps. Older permanent-split-capacitor blowers often sit in the 400 to 900 watt neighborhood at high speed. Newer ECM blowers are commonly 100 to 600 watts depending on speed. The igniter is a short spike. Electric heat strips and a heat-pump air handler are not this kit. Those are backup for a heat-pump house money.
Do not run a furnace off a light-duty indoor extension cord in the mechanical room. The cord is a heat source next to a gas appliance, and the furnace circuit is the one you put on a transfer switch or a critical-load panel, not on a daisy-chain from the kitchen.
How many watts is the three-item stack?
Write three numbers from plates, not from a chart on a van.
Fridge: running watts from the label or from EnergyGuide kWh ÷ 8,760 × a duty-cycle guess, plus a start allowance if the compressor is old. A 150-watt running fridge with a 600-watt start is a different problem than an inverter compressor that barely spikes.
Sump: 9.7 A × 115 V is about 1,100 watts running on that Zoeller class. Starting watts are higher. The pump should not start in the same second as the fridge compressor if your inverter is a 2,000-watt suitcase.
Furnace: nameplate amps × 120 V. A 6-amp PSC blower is 720 watts running, more at start. Add the inducer if it is on the same circuit.
Add running watts. Then look at the two biggest starts and whether they can miss each other. A 2,200-watt inverter that is honest at 1,800 watts rated (Honda’s EU2200i class) can hold a fridge and a furnace blower if the sump has its own battery. It will not hold fridge + sump start + furnace start. That is why the sump gets a pit battery instead of a share of the generator.
If you have a well, stop this page and use well pump on backup. Locked-rotor amps on a 230-volt submersible are how 2,200-watt inverters die.
What are the three kits, in dollars?
Kit A, no generator. Thermometers in fridge and freezer. Carbon monoxide alarms with battery backup on every level, because Ready.gov wants them anyway and a generator later will make them non-optional. A listed sump battery backup in the pit (Angi $600 to $1,200, HomeGuide $600 to $2,000+). Coolers and ice if the outage is a workday you can shop. This kit does not heat the house. It keeps you from flooding and from eating four-hour milk.
Ready.gov: generators and fuel outdoors, at least 20 feet from windows, doors, and attached garages, and working CO detectors on every level.
Kit B, carry-in power for the fridge. A 1 kWh-class power station indoors for the fridge and phones, or a small inverter generator outdoors on a heavy-duty cord to that fridge only. EcoFlow’s DELTA 2 class is 1,024 Wh and 1,800 W AC on the listing. At 150 watts average the fridge is a long night, not a three-day ice storm, unless you can recharge it. Honda’s EU2200i is 1,800 W rated, 2,200 W max, 20 feet from openings. The portable power station vs inverter page is the product class. HomeGuide still puts portables at $500 to $2,500 for the unit.
The furnace stays off Kit B unless you have a listed inlet. The sump stays on its pit battery. A cord from the inverter into a dryer outlet is still how people energize lines a lineman thinks are dead.
Kit C, those three circuits on the house. Outdoor inlet, interlock or a small transfer switch, fridge circuit, furnace circuit, and either the sump circuit or (better) the pit battery so the generator is not trying to start 9.7 amps in the rain. HomeGuide’s 2026 hookup band: inlet $20 to $100, cord $30 to $350, interlock job $400 to $850, manual transfer $400 to $1,300. The inlet box page is that hardware. The critical-load panel page is how those three breakers move.
Kit C plus a 2,200-watt inverter is the actual minimum house kit. Kit C plus a 7 kW standby is how people quietly add the well and a freezer and then call it whole-home. Sizing a standby is that next invoice.
What should three real-looking bids mean?
Bid A, sump only. Second pump, battery, charger, alarm, check valve, discharge tie-in, permit if your town wants it. Angi $900 neighborhood. If the quote is a $150 add-on battery with no second pump, you bought a charger for a pump that already failed.
Bid B, portable hookup. 30-amp inlet on the wall by the panel, listed interlock for your panel brand, generator breaker, permit. You still flip breakers so the fridge, furnace, and nothing else are on. Tape the list inside the door. This is HomeGuide’s $400 to $850 interlock band plus your generator.
Bid C, six- to ten-circuit transfer or a tiny subpanel. Fridge, furnace, sump (or skip sump if the pit battery is in), one lighting circuit, modem, maybe the garage door. Popular Mechanics’ usual manual-switch size is six to ten circuits. If Bid C includes the range and the dryer, you left the minimum kit.
If someone quotes a whole-house automatic transfer for these three loads, they sold you automatic vs manual from the wrong page.
What has to be on the quote?
Nameplate volts and amps for the furnace and the sump, written down, not “we’ll figure it in the field.”
Whether the sump backup is a second pump on a battery, or “we’ll put the existing pump on the generator.”
AHRI is not this job. The transfer equipment listing is. Inlet amperage matching the generator receptacle (L5-30 vs L14-30 vs 50-amp) belongs on the page. The 30-amp vs 50-amp cord page is that plug.
Permit, who pulls it, and a CO plan: detectors already in the house, generator 20 feet out.
What is not on the kit: well, electric strips, air conditioner, range.
How does this go wrong?
You run the fridge on a suitcase battery, skip the sump backup, and the storm that killed the power fills the pit.
You plug the furnace into a orange indoor cord because “it’s only 600 watts.”
You start the sump and the fridge compressor on the same 1,800-watt inverter and the inverter folds.
You treat USDA’s four hours as eight because the milk still smelled fine.
You buy Kit C hardware and never label the three breakers, so at 11 p.m. you turn on the kitchen lighting circuit that also has the microwave and the toaster oven.
Placement still follows generator exhaust and neighbors. A quiet inverter does not get a garage pass.
How do I decide this week?
- Put thermometers in the fridge and freezer and read them tonight so you know 37°F from 45°F before the outage.
- Photograph the furnace nameplate and the sump nameplate and write volts, amps, and watts on one card.
- If the basement takes water when it rains, price Bid A (pit battery) this week, before you shop generators.
- If you only need the fridge through a four-hour blip, Kit B (suitcase battery indoors) is enough and the generator stays in the catalog.
- If January outages last overnight and the furnace is gas, get Bid B or Bid C so the blower circuit is on a listed inlet, not on a cord.
- If you also have a well or a heat pump, this minimum kit is a layer, not the system. Use the well page or the battery-vs-standby page next, and do not pretend 2,200 watts covers them.