Storm Risk · Generator Fuel

How Much Generator Fuel to Store Safely for a Hurricane

A generator that runs out of gas at hour thirty of an outage is just an expensive lawn ornament. Here's how to work out how much fuel you actually need, how much you can safely keep on hand, and how to store it without creating a fire hazard.

Why running dry matters more than which generator you bought

Most people spend their planning energy picking the right generator and almost none on the fuel that keeps it running. Then the power goes out for three or four days, the two gas cans in the shed run dry on day two, and the sump pump or the refrigerator goes quiet right when it matters most.

The fuel question has two parts that people often mix up: how much fuel will this generator actually burn over the outage you're expecting, and how much of that fuel can you legally and safely keep at your house. Getting the first number wrong means an inconvenient trip to a gas station that may not have power either. Getting the second one wrong turns a storage shed into a fire risk. This guide walks through both, plus how to keep stored fuel usable and how to refuel without hurting yourself.

How much fuel a generator burns: a runtime illustration

Fuel burn depends on the generator's size and how much load you're actually putting on it, not just its maximum rating. Running a generator at half load instead of near its limit uses noticeably less fuel per hour and is also easier on the engine.

As a labeled illustration only, not a spec for your unit: a mid-size portable generator running essential circuits like a refrigerator, a few lights, and a sump pump at roughly half load might burn somewhere around a third to three quarters of a gallon of gasoline per hour. Over a 12-hour overnight run, that arithmetic works out to roughly 4 to 9 gallons. Your actual number could sit well outside that range depending on the model, so check the owner's manual for the listed fuel consumption at half load and full load.

Matching the generator's size to what you actually need to run changes this math directly. A generator sized for a whole house burns more per hour than one sized for a refrigerator, a few lights, and a phone charger. The honest Generator Sizing tool walks through wattage for common appliances so you can estimate a realistic load before you estimate fuel.

How much gasoline you can safely keep at home

This is where good intentions run into fire code. The National Fire Protection Association publishes guidance on storing flammable liquids around the home, and most local fire codes set limits on how much gasoline can be kept in or near an occupied dwelling, and require it be kept in approved, tightly sealed safety containers rather than open cans or non-rated jugs.

The exact quantity allowed varies by city and county, and by whether the storage is inside a garage, a detached shed, or fully outdoors. Because those limits differ by jurisdiction, check with your local fire marshal or building department for the number that applies to your address rather than relying on a figure from somewhere else.

Wherever you store it, keep gasoline away from the house's living space, away from any ignition source (water heaters, dryers, and outlets all count), and away from where the generator itself will run. This is general fuel storage guidance, not professional contractor, insurance, or engineering advice, and it doesn't replace a site-specific check from a licensed professional if you're setting up permanent storage.

Propane and diesel: different trade-offs for storage

Gasoline isn't the only option, and the storage math changes with the fuel type. The Department of Energy's consumer energy guidance covers the basics of portable and standby generator fuel types, including propane and diesel alternatives to gasoline.

Propane doesn't degrade the way gasoline does, which makes long-term storage simpler, but the tanks themselves still need to sit outdoors, away from the house, and away from any generator exhaust. Diesel has a longer shelf life than gasoline before it needs a stabilizer, and diesel generators are common for larger, longer-duration backup needs, but they typically cost more upfront. Neither fuel type gets you out of checking local storage limits: propane tanks and diesel drums both fall under their own fire code rules.

Keeping stored gasoline usable until you need it

Stored gasoline doesn't last forever. Ethanol-blended gas, which is most of what's sold at the pump, breaks down over a matter of months and can gum up a carburetor if it sits too long unused. A fuel stabilizer added at the time of storage extends how long gasoline stays usable, and rotating stock, using the oldest fuel in a vehicle and replacing it with fresh gas, keeps what's in the shed from going stale before hurricane season needs it.

Write the fill date on each container so you know at a glance what's oldest. If you're not sure how old your stored fuel is, or it's been sitting more than a season without a stabilizer, that's worth checking against the generator manufacturer's guidance before you rely on it during an outage.

Refueling safely once the storm has already hit

A hot generator and a fuel can are a bad combination. Let the unit cool completely before adding fuel, since spilled gasoline on a hot engine or muffler can ignite. Refuel outdoors, in the open air, away from the house.

Carbon monoxide is the other major risk, and it's a leading cause of death after storms when generators run indoors, in garages, or too close to windows and doors. The CDC's guidance on carbon monoxide from generators is worth reading once before the storm, not during it, so the placement rules are already second nature when the power goes out.

Timing your fuel-up matters too. The National Weather Service's hurricane safety guidance notes that gas stations often lose power or see long lines as a storm approaches, so filling containers and vehicle tanks early, well before landfall, avoids a last-minute scramble. The 48-Hour Checklist puts fuel and other prep tasks on a timeline, and the Live Storm Center tracks how much runway you actually have before conditions turn.

Questions people ask

How many gallons of gas do I need for a three-day hurricane outage?
It depends on your generator's size and how much load you're running, not just the outage length. Use your owner's manual's fuel consumption rate at half load, multiply by expected daily run hours, then multiply by the days you expect to be without power. The Generator Sizing tool can help you estimate a realistic load first.

Can I store gasoline in my attached garage?
Local fire codes typically limit how much gasoline can be stored inside or attached to an occupied dwelling, and require approved safety containers. Check with your local fire marshal for the specific limit and preferred storage location for your address.

Is propane safer to store than gasoline?
Propane doesn't degrade over time the way gasoline does, which simplifies long-term storage, but tanks still need to be kept outdoors, away from the house and away from generator exhaust. Both fuel types have their own fire code storage rules.

How long does stored gasoline actually stay usable?
Ethanol-blended gasoline can start to break down within a matter of months without a fuel stabilizer added at storage time. Rotating stock, using older fuel in a vehicle and replacing it with fresh gas, and dating each container helps you avoid relying on stale fuel during an outage.

Sources

1. NFPA: Home fire safety and flammable liquid storage
2. CDC: Carbon monoxide dangers from portable generators
3. Department of Energy: Generators and backup power basics
4. National Weather Service: Hurricane safety and preparedness

This article is educational and is not professional contractor, insurance, or engineering advice. Some links in our articles may earn us a commission at no cost to you, and never change what we recommend.