What Size Back Up Generator Do You Need for a Home?

Recommended size: 5,000–22,000W

A back up generator for a home needs 5,000 to 7,500 watts for essential circuits (fridge, freezer, lights, sump pump, WiFi, one window AC), 10,000 to 12,000 watts for nearly the whole house except central AC, or 18,000 to 22,000 watts for an automatic standby unit that runs everything including central AC. For most homeowners the best value is a 5,500W dual fuel portable such as the DuroMax XP5500HX for essentials, or a 7,500W Westinghouse WGen7500DFc for essentials plus a window AC. To run the entire house automatically the Generac Guardian 22kW standby starts itself the second the grid drops. Dual fuel models (gas plus propane) matter because gas stations often lose power in the same storm that takes out your electricity.

Back up generator size for a home by scenario

What you want to power	Generator size	Top pick
Essentials only (fridge, freezer, sump pump, lights, WiFi)	5,000–7,500W	DuroMax XP5500HX (5,500W dual fuel)
Essentials plus one window AC	7,500W	Westinghouse WGen7500DFc (7,500W dual fuel)
Whole house except central AC	10,000–12,000W	DuroMax XP12000EH (12,000W dual fuel)
Whole house including central AC (automatic)	18,000–22,000W	Generac Guardian 22kW standby

Top Pick

DuroMax XP5500HX Dual Fuel

Affordable dual fuel option with CO Alert safety shutoff and MX2 power boost technology. Runs on gas or propane for flexible fuel options during outages.

Running: 4,500W

Starting: 5,500W

Noise: 69 dB

Weight: 131 lbs

Check Price on Amazon →

What to Know About Power outage backup for a home

Partial home backup is the most common generator use case. The goal is keeping food cold, water flowing, and a few rooms comfortable until the grid comes back. A 5,000W generator handles the basics: fridge (1,200W starting), sump pump (2,000W starting), lights, and small electronics. Step up to 7,500W if you want to add a window AC unit (3,600W starting) or a space heater. Dual fuel capability is worth the small premium because propane stores indefinitely while gasoline degrades after a few months. All three models below include electric start and are transfer-switch ready for cleaner, safer hookup to your panel.

Related sizing guide

What Size Backup Generator Do You Need for a Whole House?

Sizing tables by home size and appliance load, plus a worked example and standby vs portable guidance.

Gas vs. Propane vs. Dual Fuel for Home Backup

Gasoline is available everywhere but degrades after 3 to 6 months in storage. When a major storm knocks out power, gas stations may be closed or running on their own generators with long lines. Propane stores indefinitely in sealed tanks and burns cleaner, producing less carbon monoxide. Dual fuel generators accept both, which means you can keep a propane tank ready year-round and switch to gasoline if your propane runs out. For home backup specifically, dual fuel is the strongest choice because outages are unpredictable and fuel flexibility matters most when the grid is down.

Transfer Switch: Why You Need One

A transfer switch connects your generator to your home's electrical panel safely. Without one, you run extension cords through windows to individual appliances. With a transfer switch, you flip breakers to power specific circuits (fridge, sump pump, lights, WiFi) directly from the panel. A manual transfer switch costs $200 to $400 for the hardware and $300 to $500 for a licensed electrician to install. It is a one-time investment that makes every future outage dramatically easier to manage. All three generators on this page include a 30A or 50A outlet for transfer switch connection.

How to Calculate Your Backup Load

Add the running watts of everything you want to power simultaneously. A refrigerator runs at about 150W, a sump pump at 800W, lights at 200W total, a WiFi router at 15W, and phone chargers at 25W. That puts you at roughly 1,200W running. Now add the highest single starting surge: a sump pump surges to 2,000W and a refrigerator to 1,200W. Your generator needs enough starting watts to handle the largest surge on top of the running load. A 5,000W generator covers this scenario with headroom to spare.

Running Your Generator Safely

Carbon monoxide from generators kills dozens of people every year during storm outages. Run your generator outdoors, at least 20 feet from any door, window, or vent. Point the exhaust away from the house. Install battery-operated CO detectors on every floor. Modern generators include CO shutoff sensors that automatically kill the engine if dangerous CO levels build up. Every model on this page includes this safety feature. Also ground your generator with a grounding rod if connecting to a transfer switch, and never refuel while the engine is running or hot.

Frequently Asked Questions

What size generator do I need to power my house during an outage?

For essential circuits (fridge, sump pump, lights, WiFi, phone chargers, one window AC), a 5,000 to 7,500W portable generator is the right size. For whole-house backup excluding central AC, step up to 10,000 to 12,000W. For whole-house including central AC, you need a 15,000W+ standby generator professionally installed.

What is the best backup generator for a home?

For portable home backup, the DuroMax XP5500EH (5,500W dual fuel, $550) is the best value. The Champion 7500 (7,500W dual fuel, $850) is the best mid-range option with more headroom. Both include electric start and transfer switch outlets. For permanent installation, a Generac or Champion standby unit is the professional standard.

Should I get a gas or propane generator for home backup?

Get a dual fuel generator that accepts both. Propane stores indefinitely and burns cleaner, making it ideal for emergency preparedness. Gasoline is more widely available for extended outages. Dual fuel gives you the flexibility to use whichever is available. The price premium over gas-only is typically $50 to $100.

Do I need a transfer switch for a home backup generator?

Strongly recommended. A transfer switch connects your generator to your electrical panel so you can power specific circuits (fridge, sump pump, lights) by flipping breakers instead of running extension cords. It costs $500 to $900 installed and makes every future outage safer and simpler. All generators on this page are transfer-switch ready.

What watt generator do I need to run a house?

To run essential circuits of a house you need a 5,000 to 7,500 watt generator. To run nearly the whole house except central air conditioning you need 10,000 to 12,000 watts. To run the entire house including central AC you need an 18,000 to 22,000 watt standby generator. The exact figure depends on whether the home is all-electric, has a well pump, and how many large appliances run at the same time.

What size automatic backup generator do I need for a home?

An automatic backup generator is a standby unit that starts itself within seconds of an outage and runs on natural gas or propane with no refueling. For a typical home including central AC, an 18,000 to 22,000 watt standby generator is the right size, such as the Generac Guardian 22kW, which includes a 200A automatic transfer switch. Smaller homes without central AC can use a 14,000 to 18,000 watt standby. Installation requires a licensed electrician.