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Running and starting watts for what you want powered in an outage, the generator size that covers it, and the transfer switch, hookup and permit to install it safely.
Typical figures. Check the nameplate for your model.
A soft-start kit can cut AC starting watts by 50–70%.
Typical starting points before entering your own loads.
All-electric homes (heat, range, water heater) often need 22 kW or more.
Price, convenience and fuel.
Installed prices include connection hardware and a licensed electrician.
Add the running watts of everything you want on at once, then add the extra start-up surge of the largest motor. Essentials (fridge, furnace fan, sump pump, lights) usually fit 5,000–7,500 W. Whole homes with central AC usually need 18–26 kW standby.
Running watts are the steady draw. Starting (surge) watts are the brief spike when a motor starts, often 2–3× the running watts. A generator must cover both.
A 3-ton central AC needs about 3,000 running watts and up to 9,000 to start. A soft-start kit can cut the surge by half, allowing a smaller generator.
Use a transfer switch or a panel interlock with an inlet box, installed by a licensed electrician. Never plug a generator into a wall outlet; it can backfeed and kill line workers.
A 7,500 W portable uses about 0.5–0.75 gal of gasoline per hour at half load. A 22 kW standby burns about 200–300 cu ft of natural gas per hour at half load.
Portable is far cheaper but manual and needs fueling. Standby starts on its own within seconds and runs on your gas line, which suits frequent outages, medical needs or remote homes.
Headroom handles surges and extends engine life. The calculator adds 20% over running watts for this.
Usually yes for a transfer switch, interlock or standby unit. Standby units also need gas and setback inspections.