What Is a Dual Fuel Generator and How Does It Work?
A dual fuel generator is a portable generator with an engine that can run on either gasoline or propane. You pick the fuel with a switch or selector, so you can use whatever you have on hand during an outage or a long run. An inverter version adds electronics that deliver cleaner power and let the engine adjust its speed to the load.
Westinghouse iGen12000DFcBest overall
Westinghouse WGen11500DFcHigh running watts, long runtime
Westinghouse WGen9500DFcTransfer switch ready 50AWhat "dual fuel" means
"Dual fuel" on a portable generator means one engine, two fuel choices. The usual pair is gasoline from the built-in tank and propane from an external tank (the kind many people use for a backyard grill) connected by a hose.
You will also see the term "bi fuel." On small portable units, shoppers often use it to mean the same thing: a generator that can use two fuels. In larger industrial equipment, the terms can differ. A dual fuel engine may start on one fuel and blend in a second, while a bi fuel engine runs on one fuel or the other. For home and camping generators, look at the spec sheet and check that both gasoline and propane are listed.
How a dual fuel generator works
The engine is a standard four-stroke design. It burns fuel to turn an alternator, and the alternator makes electricity. The only real difference is how fuel reaches the engine.
On gasoline, fuel flows from the tank to the carburetor or fuel system. On propane, the gas flows from the tank through a regulator and hose into the engine's air intake. A selector switch or valve chooses which source feeds the engine. Always follow your owner's manual for the exact switching steps, because they differ by model.
- Gasoline mode: the engine draws from the onboard tank, which you fill like any fuel can.
- Propane mode: the engine draws from an external tank through a regulator and hose.
- Switching: most models ask you to shut off one fuel source before using the other, so check the manual.
What makes it an inverter generator
A dual fuel inverter generator adds an inverter. The alternator makes raw power, and the inverter electronics convert it into a steady, clean output. This lets the engine speed up or slow down with demand instead of running flat out all the time.
Specs show the result. The Westinghouse iGen12000DFc lists a THD of 3% or less. THD measures how clean the power is, and lower numbers are better for phones, computers and TVs. The WGen9500DFc, a non-inverter style model on our page, lists 23% or less.
Westinghouse says its inverter models use less fuel than traditional generators because engine speed follows the load. Treat that as a manufacturer claim, and compare the runtime figures on the spec sheet instead.
Gasoline versus propane output
Propane usually gives you a little less power than gasoline. The published numbers show it clearly.
Running watts are what the generator can supply continuously. Peak watts are a brief surge for starting motors. Size your needs by running watts for steady loads, as covered on our best dual fuel generator page.
| Model | Gasoline running watts | Propane running watts |
|---|---|---|
| Westinghouse iGen12000DFc | 9,000 | 8,100 |
| Westinghouse WGen9500DFc | 9,500 | 8,500 |
| Westinghouse iGen5000DFc | 3,900 | 3,500 |
| WEN DF680iX | 5,100 | 4,500 |
Why people choose dual fuel
The big draw is flexibility. If gasoline runs short during a storm, propane may still be available, and the reverse is also true. Propane tanks also store easily, so a spare can sit ready for an emergency.
Runtime is worth a look too. Runtime is rated at 25% load, so it shows best-case use. The iGen12000DFc and WGen11500DFc list 19 hours, while the WGen9500DFc lists 12 hours. A spare propane tank can extend a run beyond the gasoline tank.
What to check before you buy
Start with the items you need to power and add up their running watts. Then compare the rest of the spec sheet. Our best generator page is a good place to see how dual fuel units sit next to other types.
Size and noise matter for camping and shared spaces. The iGen5000DFc lists 52 dBA and 105.8 lb. The three largest Westinghouse models list 64 to 74 dBA and weigh 189 lb or more.
- Running watts for the loads you must power at once.
- Runtime at 25% load, to plan refills.
- Noise in dBA and weight in pounds.
- Outlets, such as 240V for a transfer switch or interlock kit, and TT-30R for an RV.
- THD, if you will power sensitive electronics.
- A CO shutoff sensor.
Safety notes
Generators produce carbon monoxide, a gas you cannot see or smell. Run one outdoors only, well away from doors, windows and vents. Never run one in a garage, even with the door open.
Propane is flammable. Check hoses and connections for damage, keep the tank upright and outside, and keep it away from the exhaust. Let the engine cool before refueling with gasoline, and store fuel away from heat and ignition sources.
Do not plug a generator into a wall outlet to power your house. Use a transfer switch or interlock kit installed by a qualified electrician. A CO sensor is a useful backup, but it does not replace good placement. Wear hearing protection if you work near a loud unit for long periods.
Frequently asked questions
Can I run a dual fuel generator on natural gas?
Not usually. The portable models on our page list gasoline and propane. Natural gas needs a different setup, so confirm it in the manual before trying it.
Do I have to choose a fuel before I start the engine?
Yes. Pick the fuel source first, then start the engine. Follow your manual's steps for your model.
Is propane output the same as gasoline output?
No. On units that list both, propane running watts are lower, so size your load with the propane figure if you plan to rely on it.
Does a dual fuel generator need less maintenance?
It still needs regular oil changes and care as the manual describes. Propane is often described as burning cleaner, but you should still follow the maintenance schedule.