Running watts vs starting watts
Running watts is the continuous draw of an appliance. Starting watts is the brief spike — often 2-3x running watts — that motor-driven appliances like refrigerators, well pumps, and air conditioners pull for the first second or two of startup. A generator's continuous rating has to cover your total running load, and its surge rating has to cover your single largest starting spike stacked on top of everything else already running.
Totaling a real household load
Reference figures: refrigerator 600-800 running watts (surge to ~1,200-2,200W), sump pump 800-1,050W (surge to ~2,000-2,500W), window AC 1,000-1,500W, well pump 1,000-2,000W (higher surge), microwave 600-1,200W, LED lighting and phone chargers under 200W combined. Total the running watts of everything you'll run at once, then add the surge watts of only the single largest motor on that list — since motors rarely start simultaneously — to land on your target generator size.
Portable generators: backup and job-site power
Portables in the 3,000-5,000 running watt range cover a refrigerator, sump pump, some lighting, and a few electronics — solid for partial home backup or job-site power tools. Step up to 7,000-10,000 running watts and you're covering a well pump plus a window AC plus kitchen essentials at once. Portables run on gasoline or propane, need siting outdoors at least 20 feet from windows and doors due to carbon monoxide, and require manual startup with extension cords or a transfer switch.
Whole-home standby units
Whole-home standby generators, typically 14kW to 22kW+ and permanently installed with an automatic transfer switch, size to a home's full electrical panel — central AC included — for a seamless outage response. Size against your home's actual panel and peak demand (a licensed electrician calculates this precisely), not square footage. Oversizing wastes money on capacity you'll rarely use; undersizing means the unit shuts down under peak load.
Inverter generators for sensitive electronics
Powering laptops, medical equipment, or anything sensitive to power fluctuations calls for an inverter generator, which produces cleaner, more stable sine-wave power than a conventional unit. Inverter models also run quieter and more fuel-efficient at partial loads, though they cost more per rated watt and top out lower in wattage than large conventional or standby units.
Frequently asked questions
What size generator runs a fridge and a few lights?
A portable in the 2,000-3,000 running watt range comfortably covers a refrigerator's running and starting watts plus lighting and small electronics, with headroom to spare.
Will a 5,000-watt generator run central air?
Only a small window or portable AC unit. A central AC compressor's starting watts (often 3,000-5,000W alone) typically overwhelm a 5,000W generator once other household loads stack on, so central air generally needs a larger portable or whole-home standby unit.
Should I buy extra headroom beyond my calculated load?
Add 10-20% headroom above your calculated peak load. Running a generator at its absolute ceiling continuously shortens engine life and leaves no margin if you add an appliance later.
Do I need a transfer switch?
Yes, for any generator powering household circuits during an outage. A transfer switch isolates your home from the utility grid, protecting utility workers and preventing backfeed damage, and it's required by electrical code for permanent hookups.