Recommended size: 15,000–22,000W+
An automatic backup generator is a permanently installed standby unit, and a 15,000–22,000W+ model is what you need for whole-home backup including central AC. These permanently installed units start automatically within seconds of a power outage and run on natural gas or propane, so there is no refueling. They include a 200A transfer switch for direct panel connection.
Market-leading whole-home standby generator. Includes 200A transfer switch. Powers everything including central AC automatically when the grid goes down.
Central AC draws 10,500+ starting watts on its own, which pushes the total home load past what any portable generator can handle reliably. Standby generators solve this by delivering 15,000–22,000W+ continuously from a permanent installation connected to your home's natural gas line or a large propane tank. They start automatically when the grid goes down and switch back when power returns. Installation requires a licensed electrician and typically costs $500–$1,500 on top of the unit price. The 200A transfer switch included with both models below handles the full capacity of most residential electrical panels.
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Sizing tables by home size and appliance load, plus standby vs portable guidance.
An automatic backup generator, also called a standby or automatic home generator, sits on a pad outside the house and is wired to the electrical panel through an automatic transfer switch. When utility power drops, the transfer switch senses the loss, isolates the house from the grid, and signals the generator to start. Within about 10 seconds the house is back on generator power with no one touching anything. When the grid returns, the switch waits for stable utility voltage, transfers the house back, and lets the generator cool down and shut off. The unit also runs a short self-test every week so it is ready when the outage comes.
Residential standby generators run from about 10,000W to 26,000W. The deciding load is central air conditioning: a 3 to 5 ton AC compressor needs 10,000W or more to start, on top of everything else in the house. For a typical home with central AC, an 18,000 to 22,000W unit like the Generac Guardian 22kW or Champion 22kW covers the whole panel, which is why 22kW is the most common residential size. A smaller home without central AC, or one willing to shed the AC during an outage, can use 10,000 to 14,000W. If the house is all-electric with an electric range, electric water heater and a well pump, or has two AC units, plan on 24,000W or more, or have the installer set up load management so the largest loads take turns.
Standby generators burn natural gas or propane, never gasoline, so there is nothing to refuel during a long outage. If the house has a natural gas line, that is the simplest and cheapest fuel: supply is effectively unlimited and the gas utility rarely fails in the same storm that takes down power lines. Without a gas line, a 250 to 500 gallon propane tank feeds the generator; a 22kW unit at half load burns roughly 2 gallons of propane per hour, so a 500 gallon tank (filled to 80 percent) runs about 8 days. Most units are rated slightly lower on natural gas than on propane, so check the natural gas rating when sizing.
Unlike a portable, a standby generator is a permanent installation: a concrete or composite pad, a gas line sized for the unit, the automatic transfer switch wired into the panel, and an electrical and gas permit with inspection. Both picks on this page ship with a 200A automatic transfer switch, which matches the main breaker in most homes. Installation typically adds $500 to $1,500 for a straightforward setup near the panel and gas meter, and more where a long gas run, a gas meter upgrade, or trenching is needed. Budget for a licensed electrician and a licensed gas fitter; this is not a homeowner install.
An automatic backup generator is a standby generator that is permanently installed outside the house, connected to natural gas or propane, and wired to the electrical panel through an automatic transfer switch. It starts on its own within seconds of a power outage and shuts off when the grid returns, with no manual start and no refueling.
For a whole home including central AC, an 18,000 to 22,000W standby generator is the standard size; the Generac Guardian 22kW and Champion 22kW both come with a 200A transfer switch. Homes without central AC can use 10,000 to 14,000W. All-electric homes or homes with two AC units need 24,000W or more, or load management.
The 22kW units on this page run about $5,000 to $6,500 for the generator and transfer switch. Installation typically adds $500 to $1,500 for a simple setup near the panel and gas meter, and more where a long gas line, meter upgrade, or trenching is required, so plan on roughly $6,000 to $10,000 all in for a whole-home system.
A standby generator is better if you want the house to stay powered with no one home, need central AC during outages, or have frequent multi-day outages. A portable is better on cost: a 7,500W dual fuel portable with a manual transfer switch covers the essentials for a fraction of the price, but someone has to roll it out, start it, and refuel it.
On natural gas, as long as the outage lasts, with an oil change roughly every 200 hours of runtime. On propane, runtime depends on the tank: a 22kW unit at half load uses about 2 gallons per hour, so a 500 gallon tank runs about 8 days and a 250 gallon tank about 4 days.
| Generator | Starting W | Running W | Fuel | Noise |
|---|---|---|---|---|
| Generac Guardian 22kW Standby | 22,000W | 22,000W | Natural Gas / Propane | 67 dB |
| Champion 22kW aXis Standby | 22,000W | 22,000W | Natural Gas / Propane | 67 dB |
Generac
★4.2
Market-leading whole-home standby generator. Includes 200A transfer switch. Powers everything including central AC automatically when the grid goes down.
Champion
★4.2·249 ratings
Strong Generac alternative with 200A transfer switch included. Competitive pricing and quiet 67 dB operation for whole-home backup.
The accessories most generator owners add to run safely and connect to the house.
Transfer / Interlock
★4.7·1,733 ratings
Lets you safely back-feed your panel from one inlet. Confirm it matches your breaker brand and amperage.
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Power Cord
★4.8·2,827 ratings
Heavy 10-gauge twist-lock cord rated to 7,500W, the standard link between a portable unit and your inlet box.
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Weather Cover
★4.6·2,107 ratings
Keeps rain and snow off the unit so you can run it through a storm with proper ventilation.
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CO Safety
★4.7·19,762 ratings
Generator exhaust is the top cause of CO poisoning during outages. A battery alarm keeps working when the grid is down.
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Fuel Care
★4.8·35,997 ratings
Treats 40 gallons and keeps stored fuel fresh for up to 24 months so the engine starts when you need it.
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