The short answer: a dual fuel generator runs on either gasoline or propane, and you choose the fuel each time you use it. Gasoline gives you a little more power and is easy to find before a storm, but it goes stale and is messy to store. Propane gives you a little less power, but it keeps for years in a sealed tank, burns cleaner and is usually easier to stockpile. For home backup, having both is the real advantage: when one fuel is scarce after a storm, you can switch to the other. This guide explains the differences, how to choose, and how to store each fuel safely.
What is a dual fuel generator?
A dual fuel generator is a portable or inverter generator with an engine that can burn two fuels: gasoline from its built-in tank, or propane (LP gas) from a separate cylinder connected by a hose and regulator. A selector switch or knob tells the engine which fuel to use. Some models can switch fuels while running; others need to be shut down first. A few "tri-fuel" models add a natural gas connection, which has to be installed by a licensed gas fitter or plumber.
Dual fuel units come in two main types:
- Conventional open-frame generators: louder, heavier and usually more watts for the money. Good for running a fridge, sump pump and well pump together.
- Inverter dual fuel generators: quieter, more fuel-efficient at light loads, and they produce cleaner power for laptops, TVs and other electronics. Our guide on inverter vs. regular generators covers that choice in detail.
You can browse both types in our inverter and dual fuel generators collection.
Gasoline vs. propane at a glance
| Gasoline | Propane | |
|---|---|---|
| Power output | Full rated output | Usually somewhat lower (check the spec sheet) |
| Energy per gallon (EIA) | About 120,214 Btu | About 91,452 Btu |
| Storage life | Short; breaks down over months, slower with stabilizer | Does not go stale in a sealed, well-kept tank |
| Availability in an outage | Gas stations need power to pump | Cylinder exchanges and refills, but can run short before big storms |
| Engine maintenance | Carburetor can gum up if fuel is left in | Burns cleaner, less carburetor trouble |
| Cold weather | Starts reliably | Tank pressure drops in deep cold |
Power output: why propane gives you fewer watts
Propane holds less energy than gasoline. According to the U.S. Energy Information Administration (EIA), a gallon of motor gasoline contains about 120,214 Btu, while a gallon of propane contains about 91,452 Btu, roughly a quarter less. That is why almost every dual fuel generator lists two sets of numbers: one for gasoline and a lower one for propane.
In practice, this matters most when you are close to your limit. If your essential loads only just fit on the gasoline rating, they may not fit on propane, especially when a refrigerator compressor or well pump kicks on and needs its starting surge. When you size a dual fuel unit, size it using the propane rating, so you are covered no matter which fuel you have. Our guide on what size generator you need walks through the math with a worksheet.
Run time and fuel use
Run time depends on the size of the generator, how much load you put on it, and how much fuel you have on hand, so there is no single number that fits everyone. A few things are true in general:
- Light loads stretch fuel. A generator running at a quarter or half of its capacity burns far less fuel per hour than one running near full output. Inverter models are especially good at this because the engine slows down when demand drops.
- Propane is easy to stack up. Because it does not go stale, you can keep several full cylinders on hand and swap them as each one runs out. Larger cylinders or a properly installed tank extend run time further.
- Gasoline is limited by what you can safely store. Most households only keep a few cans, and refilling during a widespread outage can be hard.
Your generator's manual lists run time at a given load for each fuel. Use those figures for your planning, and assume real-world run time will be a little lower.
Storage, shelf life and availability
This is where propane earns its place in a home backup plan.
Gasoline begins to break down over time and can leave varnish in the carburetor, which is one of the most common reasons a generator will not start after sitting in the garage. A fuel stabilizer slows this down, and many owners rotate their stored gas into the car every few months. During a regional outage, gas stations without backup power cannot pump, and lines can be long at the ones that can.
Propane does not go stale in a sealed cylinder that is in good condition, so you can buy it in calm weather and keep it ready. Cylinders are easy to refill or swap at many hardware stores and gas stations, although exchange racks can empty quickly before a forecast storm. Running the generator on propane between uses also helps avoid carburetor problems, since there is no liquid fuel left sitting in it.
For a full checklist of what to keep on hand, see our guide on how to prepare for a power outage.
Safety: carbon monoxide, fuel storage and home connections
Both fuels produce carbon monoxide (CO), a gas you cannot see or smell. Propane burns cleaner than gasoline, but it is not safe indoors. Ready.gov advises that generators should always be used outdoors and at least 20 feet away from windows, doors and attached garages, and that every level of your home should have working CO detectors. Never run a generator in a garage, basement, shed or porch, even with the door open.
Fuel storage rules to follow:
- Propane cylinders stay outdoors. The Missouri Propane Safety Commission, like other propane safety groups, says never to store or place a propane cylinder indoors or in an enclosed area such as a basement, garage, shed or tent. Keep cylinders upright, with the valve closed and capped when not in use. Larger tanks and quantities are governed by NFPA 58 and your local fire code, so check with your fire department or propane supplier.
- Gasoline goes in approved fuel containers, stored away from the house, living spaces and anything that can spark, in quantities your local fire code allows.
- Refuel only when the engine is off and cool. Ready.gov also advises letting the generator cool before refueling, since spilled fuel on a hot engine can ignite.
Connecting to your home: plugging appliances directly into the generator with heavy-duty outdoor extension cords is the simplest option. If you want to power circuits in your electrical panel, you need a transfer switch or interlock kit, and it must be installed by a licensed electrician following local code and permits. Never back-feed power through a dryer outlet or any wall outlet with a double-ended "suicide cord". It is illegal, it can start a fire, and it can send electricity back into utility lines and kill line workers. Our guide to transfer switches vs. interlock kits explains the safe options.
Which fuel should you use?
With a dual fuel generator you do not have to pick one forever. A simple approach that works for most homes:
- Make propane your stored backup fuel. Keep a few full cylinders outside, ready to go, because propane does not go stale.
- Use gasoline when you need maximum power or when you can easily buy fresh fuel, then run the carburetor dry or switch to propane before storage.
- Size for propane. Make sure your must-run appliances fit within the propane rating.
- Test both fuels a few times a year under a light load so you know the generator starts on each.
If you live in an apartment or condo where fuel storage and generator use are restricted, a battery-based option is often a better fit. See our portable power stations and options for condos and apartments. For quiet, fuel-free backup at home, a home battery backup system can work alongside a generator or replace it for shorter outages. Our guide on standby vs. portable vs. solar generators compares the bigger picture.
FAQ
Is a dual fuel generator worth it for home backup?
For most homeowners, yes. Being able to switch fuels means you are not stuck if gas stations are closed or propane exchanges are sold out, and storing propane long term is easier than storing gasoline. The trade-off is a slightly lower output on propane, which you can plan for by sizing on the propane rating.
Does a generator produce less power on propane?
Usually, yes. Propane contains about a quarter less energy per gallon than gasoline, according to EIA figures, so dual fuel generators list a lower running and starting wattage on propane. Check the spec sheet for both numbers.
Can I switch from gasoline to propane while the generator is running?
Some dual fuel generators allow switching while running, and others must be shut off first. Follow the instructions in your manual, and never connect or disconnect a propane cylinder near a hot engine or open flame.
Is propane safer to run indoors than gasoline?
No. Any fuel-burning generator produces carbon monoxide. Run it outdoors only, at least 20 feet from windows, doors and attached garages, as Ready.gov advises, and keep working CO detectors on every level of your home.
Can I store propane tanks in my garage?
No. Propane safety groups advise never storing cylinders indoors or in enclosed spaces like garages, basements or sheds. Keep them outside, upright and away from the house's openings, and follow NFPA 58 and your local fire code for larger quantities.
Not sure whether a dual fuel generator, a power station or a battery system is right for your home? Email us and we will help you think it through.
This guide is general information, not electrical advice. Anything connected to your home’s wiring should be installed by a licensed electrician and checked against local code.