AmpSizerWhat has to stay on when the power goes?
An outage plan is a list of decisions made in advance. Made during the outage, in the dark, it is a list of regrets.
One circuit check a month
MonthlyOne thing a month worth measuring, testing or recalculating on a home electrical system — the part of sizing that happens after the install. No product pitches, and nothing that needs a live panel.
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How this works
Running and starting watts, by appliance
What each load draws continuously and what it demands for the first second, which is the number that stalls generators.
| Load | Running watts | Starting surge |
|---|---|---|
| Refrigerator or freezer | 150–800 W | 1,200–2,200 W |
| Furnace blower, 1/2 HP | 600–900 W | 1,800–2,400 W |
| Well pump, 1/2 HP | 800–1,000 W | 2,000–3,000 W |
| Sump pump | 800–1,050 W | 1,500–2,900 W |
| Window air conditioner | 900–1,200 W | 2,000–3,000 W |
| Lighting, whole floor in LED | 100–300 W | none |
| Microwave | 1,000–1,500 W | none |
| Electric water heater | 4,500 W | none |
Only the largest starting surge counts. Two large motors starting in the same instant is rare enough that sizing for it buys roughly twice the generator you need.
Frequently asked questions
Do I add every starting surge together?
No, only the largest one. Motors start at unrelated moments and the chance of two large compressors coinciding is small enough that the industry sizes on the biggest single surge. Adding them all gives roughly double the generator, at roughly double the price and the fuel.
Can I back up electric heat or an electric range?
Rarely on a portable. Each is 4 to 9 kilowatts on its own, which is most of a mid-size generator before anything else is connected. This is why outage plans concentrate on refrigeration, heating controls, water and lighting, and why whole-house standby units start much larger.
Does a transfer switch matter for the plan?
It matters for the install rather than the arithmetic, and it is not optional: backfeeding a panel through a receptacle energises the utility side and is lethal to line workers. Budget the transfer switch or interlock as part of the generator, because it is part of the generator.