PowerProof Home Work Anywhere. Roam Everywhere. Live Free.

Backup Generators for Home: Sizing, Types, Transfer Switches and Safety

Portable, inverter, dual fuel and standby generators explained, plus transfer switches, interlock kits and safe operation.

A backup generator is still the most practical way to keep a whole home’s essentials running through a multi-day outage. But generators vary enormously, from a quiet 2,000-watt inverter that runs a fridge and lights to a 24-kilowatt standby unit that powers central air automatically. This hub explains how to choose the right type and size, how to connect it to your home safely, and how to keep it ready.

Start with your loads, not the generator

Every sizing decision starts with what you need to run at the same time. Add the running watts of each essential appliance, then add the largest starting surge from any motor, such as a refrigerator compressor, sump pump or well pump. Motors briefly draw two to three times their running watts when they start. A generator that covers the running total but not the surge will stall or trip its breaker the moment the pump kicks on.

The Home Generator Size Calculator does this math for you and shows the steps. Use the wattages on your own appliance labels; the defaults are typical figures from manufacturers’ wattage guides, not measurements of your home.

Types of home generators

Conventional portable generators

Open-frame portable generators offer the most watts per dollar. They are loud, they must run outdoors, and their power quality is fine for most appliances but not ideal for sensitive electronics unless the manufacturer states low total harmonic distortion. They are the usual choice for running a fridge, freezer, sump pump and furnace blower through a transfer switch or interlock.

Inverter generators

Inverter generators produce clean, stable power suited to computers and modern appliances, run much more quietly, and throttle the engine down at light loads to save fuel. They cost more per watt and most top out at a few thousand watts, although larger inverter models now reach the size of conventional portables.

Dual fuel and tri-fuel generators

Dual fuel models run on gasoline or propane. Propane stores for years without going stale and is often easier to keep on hand in quantity, but it produces somewhat less power than gasoline in the same engine, so check both ratings on the spec sheet. Tri-fuel models add natural gas.

Whole-house standby generators

Standby generators are permanently installed outside, run on natural gas or propane, and start automatically through an automatic transfer switch within seconds of an outage. They are the most convenient option and the most expensive, because the price includes the unit, the transfer switch, a concrete or composite pad, gas and electrical work, and permits. Get several written quotes that itemize installation.

Connecting a generator to your home

You have three safe choices. You can run extension cords from a portable generator to individual appliances, using heavy-duty outdoor cords rated for the load. You can have an electrician install a manual transfer switch that powers selected circuits. Or you can have an electrician install a generator interlock kit on your main panel, which mechanically prevents the main breaker and the generator breaker from being on at the same time.

What you must never do is backfeed the house through an outlet with a double-male cord. Besides being illegal in most places, it can energize the utility lines and endanger line workers. The Transfer Switch Selector compares the options for your situation.

Generator safety

Carbon monoxide from generator exhaust kills people every year, often during the first days after a storm. The CDC and the Consumer Product Safety Commission are clear: never run a generator inside a home, garage, basement, crawlspace or shed, even with doors open. Keep it at least 20 feet from the house with the exhaust pointed away from doors, windows and vents, and install battery-backed carbon monoxide alarms on every level. The CPSC advises choosing a portable generator that shuts off automatically when carbon monoxide builds up; models certified to the PGMA G300-2018 or UL 2201 safety standards include this protection.

Let the engine cool before refueling, store fuel in approved containers away from living spaces, and keep the generator dry. Most manufacturers sell or recommend a running cover for wet weather.

Fuel and runtime

Runtime depends on load, fuel and tank size. Manufacturers publish runtime at a stated load, usually 25 or 50 percent. Gasoline goes stale in months unless treated with stabilizer, so rotate it. Propane cylinders store for years, and a standby generator on natural gas runs as long as the utility supplies gas. Plan how many days you want to cover and how much fuel that means before you buy.

Maintenance

A generator that sits for a year often will not start when you need it. Follow the owner’s manual for oil changes, spark plug and air filter service, and exercise it monthly under some load. Standby units run a scheduled self-test, but they still need annual service.

Tools for this topic

Latest Backup Generators guides

New guides are added as they pass our fact-check. Browse everything in Backup Generators, or get new guides by email.

Sources we rely on

Frequently asked questions

What size generator do I need to run my whole house?

Whole-house coverage including central air conditioning often needs a standby generator in the range of 14 to 26 kilowatts or more, depending on the home. Running only essentials usually needs far less. Add up the running watts of what you need at once plus the largest starting surge.


Can I run a generator in my garage with the door open?

No. Carbon monoxide builds up quickly even with the garage door open. Run portable generators outdoors only, at least 20 feet from the home, with the exhaust pointed away from doors, windows and vents.


Is an interlock kit as safe as a transfer switch?

A listed interlock kit installed by a licensed electrician on a compatible panel prevents backfeeding in the same way, by making it impossible to turn on the main breaker and the generator breaker together. It is often cheaper but requires you to manage which breakers are on.


How often should I run my generator?

Most manufacturers recommend running a portable generator for a short period every month, ideally with some load connected, and servicing it per the owner’s manual. Standby generators run an automatic weekly or monthly exercise cycle.