How the generator calculator works
Running watts + the biggest surge
Generators are rated in running watts (continuous output) and starting watts (brief surge capacity). Motors — fridges, pumps, furnace fans, AC compressors — draw 2–3× their running draw for a second at startup. The correct sizing math, and the one electricians use: sum all running watts, add the single largest surge on top (motor starts stagger in reality), then keep ~20% headroom. Summing every surge simultaneously is how people get talked into double the generator they need.
The three classes
- 2,000–3,500W inverter: fridge, lights, phones, router — the "fridge and Wi-Fi" class. Quiet, clean power safe for electronics, sips fuel.
- 5,000–7,500W: the outage workhorse — adds the well pump or furnace fan, maybe a window AC. Powers through a transfer switch for selected circuits.
- 10,000W+ standby: whole-house including central AC and electric water heat. Installed permanently; this is installer territory.
Safety is not optional
Never connect a generator to house wiring without a transfer switch — backfeeding power lines can kill utility workers. Run portable units outdoors, 20+ feet from windows, never in a garage (CO kills quietly). Fuel math: a 3,000W inverter load at ~50% runs roughly 6–10 hours per gallon — plan storage accordingly, and rotate gasoline stock (it ages).