Storm Risk · Generators
How Many Watts You Need to Run Essentials in a Blackout
A dead refrigerator, a silent sump pump, or a medical device with no charge turns a power outage into a real problem fast. This guide shows you how to add up the actual watts your household needs, and where that math has limits.
- Why 'just buy a generator' isn't a plan until you have a number
- Running watts vs. starting watts: the number on the box isn't the whole story
- What essential appliances typically draw (a labeled illustration, not a guarantee)
- Building your own list: the arithmetic that actually protects your household
- Where this math breaks down: the safety limits no wattage chart covers
- What to check next before the next storm watch
Why 'just buy a generator' isn't a plan until you have a number
When the power goes out in a storm, the appliances that matter most aren't your TV or your microwave. They're the ones that keep food safe, keep a basement dry, or keep a medical device running. Guessing at a generator or battery size, or buying whatever is in stock at the hardware store, often means either overspending on capacity you don't need or coming up short when a sump pump and a refrigerator try to start at the same time.
This article walks through the difference between running watts and starting watts, gives labeled examples of what common household items draw, and shows you how to build your own list. It also covers where the math runs into real safety limits that matter more than the number on the box.
This is not professional contractor, insurance, or engineering advice.
Running watts vs. starting watts: the number on the box isn't the whole story
Every appliance has a running wattage, which is what it draws once it's operating steadily. Anything with a motor, like a refrigerator, sump pump, well pump, or air conditioner, also has a starting wattage (sometimes called surge wattage), which is a short burst of extra power needed just to get the motor moving. That surge can run several times higher than the running wattage for a second or two.
This matters because a generator or battery has to cover your total running watts for everything you plan to use at once, plus the single highest starting surge among those items (since motors rarely all start at the exact same instant). A generator rated for less than that combined figure will stall or trip when the sump pump kicks on.
What essential appliances typically draw (a labeled illustration, not a guarantee)
Every model is different, and the only number you should fully trust is the one printed on your own appliance's nameplate or in its manual. But as a rough illustration of scale, here's how common essentials tend to compare in running watts, with starting watts in parentheses where a motor is involved:
Refrigerator/freezer: roughly 100 to 200 running watts (start surge often 600 to 1,200 watts). Sump pump: roughly 800 to 1,500 running watts (start surge can exceed 2,000 watts). Furnace blower fan: roughly 300 to 900 running watts (motor start surge included). Window air conditioner: roughly 500 to 1,500 running watts depending on size. Sump pump, well pump, and furnace fan rarely all start at the same second, but plan as if two might.
A few LED lights and phone/medical device chargers: typically well under 100 watts combined. A CPAP machine: often 30 to 60 watts, though older or heated humidifier models draw more.
These are illustrations to help you picture scale, not a substitute for checking your own equipment. The Department of Energy has more detail on how appliance energy use is measured and labeled.
Building your own list: the arithmetic that actually protects your household
Start by writing down every appliance or device you'd want running during an outage, in order of importance. For each one, note its running watts (from the nameplate, not a guess) and, if it has a motor, its starting watts.
Add up the running watts of everything you'd run at the same time. Then add the single highest starting-watt figure among your motor-driven items to that total. That combined number is roughly what your power source needs to handle. If you're not sure how to translate that into a generator size, the honest Generator Sizing tool walks through the same math with your specific appliance list.
It also helps to separate 'must run continuously' items (medical devices, sump pump, refrigerator) from 'nice to have intermittently' items (lights, phone chargers, a fan). Many households size their backup power for the first group and treat the rest as bonus capacity.
Where this math breaks down: the safety limits no wattage chart covers
Getting the number right doesn't mean the power is safe to use however you like. Portable generators produce carbon monoxide, a gas you cannot see or smell, and running one in a garage, basement, or near open windows can be fatal within minutes. CDC guidance on carbon monoxide poisoning is worth reading before you ever plug one in, and manufacturer instructions on generator placement should be followed exactly.
Overloading a single circuit or extension cord is another real risk, separate from whether your total generator wattage is sufficient. Cords rated for light use can overheat under a sump pump's draw even if the generator itself has plenty of capacity left. If you plan to connect a generator to your home's wiring rather than running extension cords to individual appliances, that connection needs to go through a transfer switch installed by a licensed electrician, not a direct plug into a household outlet.
Battery backups avoid the carbon monoxide risk entirely but usually hold less total capacity, so the math shifts toward runtime (how many hours you can sustain the load) rather than just peak watts. Either way, the wattage total is only step one; how the power reaches your appliances safely is step two.
What to check next before the next storm watch
Once you have a wattage total, the next useful step is matching it against your actual risk. The free 3-Minute Storm Readiness Check can help you see how your household's outage plan compares against common gaps, and the 48-Hour Checklist gives you a countdown of what to charge, fill, and secure once a watch is issued for your area.
Officials, not this site, call the actual watches, warnings, and evacuation orders. For real-time storm tracking, the National Weather Service safety pages and ready.gov guidance on power outages are good places to confirm what's happening in your area and what officials are recommending right now.
Add up your own list with the honest Generator Sizing tool, and plan the rest of the outage with the Supply Calculator.
Questions people ask
How many watts does a typical house need to run everything during an outage?
There's no single figure, since it depends entirely on which appliances you choose to keep running. A household covering just a refrigerator, sump pump, and some lights and charging needs far less than one also running a window air conditioner or electric heat. Add up your own list's running watts plus the highest single starting surge to get a household-specific number.
Can I just add up the wattage labels on my appliances?
That's the right starting point for running watts, but motors (like those in a refrigerator, sump pump, or furnace fan) also draw a short burst of extra starting watts that many labels don't show clearly. Check the appliance manual or nameplate for a starting or surge wattage figure, and plan your generator or battery around the combined total, not just the running number.
Is a battery backup or a generator better for essential appliances?
Each has different tradeoffs: generators can often sustain higher loads for longer if fuel is available, but they produce carbon monoxide and must be run outdoors, away from windows, according to CDC guidance. Battery backups avoid that risk but usually have a fixed capacity that runs down, so runtime becomes the limiting factor instead of peak wattage.
Sources
This article is educational and is not professional contractor, insurance, or engineering advice. Some links in our articles may earn us a commission at no cost to you, and never change what we recommend.
