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Gas generators: choosing one and keeping it ready

By the Plain Prepper editors. Updated 2026-10-14.

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Quick answer

A gasoline portable generator is the most common outage backup, and gas is easy to buy until a storm closes the stations. Size it by adding your running watts plus the largest starting watts. Pick one with a carbon monoxide shut-off. The catch is fuel life: Generac says untreated fuel stored over 30 days can go bad. Champion says gasoline can clog a carburetor within two weeks if it is not used or drained. Use stabilizer, run the generator monthly, and always run it outdoors at least 20 feet from the house.

Gas, propane or dual fuel

Gasoline gives the most power from a given engine. Champion says propane typically delivers about 10% less wattage than gasoline. Propane does store longer and burns cleaner. A gas-only generator is simple and makes full power, but you are tied to fuel that does not keep.

Fuel	Strength	Weak spot
Gasoline	Full rated power, easy to buy	Short storage life, stations close in storms
Propane	Stores longer, cleaner burning	About 10% less wattage
Dual fuel	Switch fuels as supply allows	Size from the lower propane rating

If fuel storage worries you, see our dual fuel generator guide.

How big a gas generator you need

Start from a list of what must run, total the running watts, then add the single biggest starting load. Champion's rule of thumb puts most 2,000 square foot homes at 5,000 to 7,500 watts and says central air pushes the need to 10,000 or more. For a fridge plus some lights and phone chargers, Champion says 3,500 watts is enough. Our generator for your house guide has a worked example.

Keeping gasoline usable

Fuel that has gone bad can keep a generator from starting when you need it. The makers' own numbers:

• Generac: fuel stored over 30 days without a stabilizer can deteriorate and damage fuel system parts. Properly prepared fuel can be stored for up to 24 months.
• Champion: with stabilizer, in a cool, dry place, gasoline has a maximum shelf life of up to one year. Left in the carburetor, gas can clog it within two weeks if it is not used or drained.
• Champion: use ethanol-free (REC-90) gasoline whenever possible. With standard pump gas, never let it sit in the tank more than 30 days without a high-quality stabilizer.

Generac's storage steps are to treat the fuel, open the fuel valve, start the engine, and run it for 30 minutes. That circulates the stabilizer through the system. If fuel was not treated, Generac says to drain it into an approved container.

A simple maintenance routine

Champion's maintenance checklist boils down to a few habits:

• Break-in: change the oil right after the first five hours.
• Oil: 100 hours is roughly a year of typical use or one long outage. Champion suggests halving that interval in dusty or hot conditions.
• Monthly run: start the unit once a month and run a few high-draw items for 15 to 20 minutes.
• Spark plug: replace it once a year.
• Air filter: replace paper filters. If you cannot see light through one, it is time.

Storing gas cans safely

NFPA's generator safety sheet says to store generator fuel only in a container made for the purpose and labeled as such, and to keep the containers outside living areas. Turn the generator off and let it cool before refueling. Never refuel it while it is hot.

Run it where carbon monoxide cannot reach you

Gasoline engines make carbon monoxide, and the Consumer Product Safety Commission counts about 100 U.S. deaths a year from portable generator CO. Its placement rule is the one to memorize: outside only, 20 feet or more from the house. Garages, basements, crawlspaces, sheds, porches and carports are all off limits, even with the doors up. Aim the exhaust away from anything that opens into the home, and favor a model that shuts itself off when CO builds up. NFPA's tip sheet adds one more layer: CO alarms inside the house.

What to look for when you buy

Questions people ask

How long can gas sit in a generator?

Champion says gas can clog the carburetor within two weeks if it is not used or drained. Generac says fuel over 30 days without stabilizer can deteriorate. With stabilizer and proper prep, Generac says up to 24 months.

Should I use ethanol-free gas in a generator?

Champion recommends ethanol-free (REC-90) gasoline whenever possible. With standard pump gas, it says never let it sit over 30 days without a high-quality stabilizer.

How often should I run my generator?

Champion suggests once a month, under a load such as a space heater or hair dryer, for 15 to 20 minutes.

Is a gas generator better than propane?

Gas gives the engine's full rating. Champion puts propane about 10% lower in output, though propane keeps longer in storage and burns cleaner.

Sources

• Portable Generator Storage and Preparation, Champion Power Equipment
• Portable Generator Maintenance Schedule and Checklist, Champion Power Equipment
• What Size Generator Do I Need?, Champion Power Equipment
• How Do I Prepare My Portable Generator for Storage?, Generac
• Generator Safety tip sheet, National Fire Protection Association
• As Winter Storms Threaten Millions in the U.S., CPSC Issues Safety Tips, U.S. Consumer Product Safety Commission

Sources checked 2026-10-14.