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A tri-fuel generator runs on gasoline, propane or natural gas, switching between them with a selector or by connecting a different supply. On paper it sounds like the ultimate backup: if you run out of one fuel, grab another. In practice, the value depends heavily on whether you actually have a natural gas line you can safely connect to, and whether you understand the output penalty each fuel brings. This explainer covers how tri-fuel machines work, who genuinely benefits, and the installation details that decide whether the third fuel is useful or just a line on the spec sheet.
How a tri-fuel generator works
Most tri-fuel portables start as a gasoline engine with a carburetor, then add a gaseous fuel regulator and mixer that feeds propane or natural gas vapor into the intake. Some are factory-built as tri-fuel; others are gasoline generators with aftermarket conversion kits. Factory units typically include a fuel selector, a propane hose with regulator, and an inlet fitting for a natural gas quick-connect. Switching fuels generally means shutting down or at least following a set sequence, not flipping a switch mid-run.
Why natural gas produces less power
Natural gas carries less energy per cubic foot than propane carries per equivalent volume of vapor, and household gas pressure is low. The engine simply receives less energy per intake stroke. Expect output on natural gas to be meaningfully lower than on gasoline, often somewhere in the range of 10 to 25 percent less depending on the engine and the gas supply.
Output by fuel: an illustrative example
The numbers below use a hypothetical generator rated around 9,000 running watts on gasoline to show typical derating patterns. Check the spec sheet of any specific model for its published figures.
| Fuel | Illustrative running watts | Approx. derate vs gasoline | Fuel supply | Storage concern |
|---|---|---|---|---|
| Gasoline | ~9,000 W | 0% | Cans, finite | Degrades in months |
| Propane | ~8,100–8,500 W | ~5–10% | Cylinders or tank | Stores indefinitely |
| Natural gas | ~6,800–7,700 W | ~15–25% | Utility line, continuous | None, but depends on utility pressure |
The natural gas connection is the whole point
The reason to pay extra for tri-fuel is natural gas: an effectively unlimited supply piped to your house that does not need hauling, storing or refilling. Natural gas service usually stays on through electrical outages, although it is not guaranteed, particularly after earthquakes or major floods. With a proper connection, a tri-fuel portable can run for days without a fuel run.
What a safe connection involves
A permanent outdoor gas stub-out with a shutoff valve and a quick-connect fitting, installed by a licensed gas fitter or plumber, is the standard approach. The gas meter and piping must be able to supply the generator’s demand in addition to your furnace, water heater and range. A generator in the 7,000 to 10,000 watt range may demand somewhere around 100 to 150 cubic feet per hour or more at load; the fitter will size the line accordingly. Many jurisdictions require a permit. Budget roughly $300 to $1,500 for a stub-out depending on distance from the meter and local labor rates, and confirm the price locally.
What not to do
Do not improvise by tapping a grill line or running a long flexible hose through a window or door. Poorly sized lines starve the engine, and leaks are a fire and explosion risk. The generator itself still needs to sit at least 20 feet from the house with exhaust pointed away from openings, so the stub-out location matters.
Who benefits and who does not
Good fit
- Homes with existing natural gas service and a suitable outdoor location for a stub-out 20 feet or more from the house.
- Areas with multi-day outages where hauling gasoline is impractical.
- Owners who want a cheaper path than a permanent standby unit, which often costs several times more installed.
Poor fit
- Homes without natural gas; a dual-fuel gas/propane unit costs less and does the same job.
- Renters or anyone who cannot install a permanent gas fitting.
- Owners who need maximum output, because natural gas derating may force you up a size class.
Electrical connection still matters
A tri-fuel portable connected to house circuits needs the same safe setup as any other: a manual transfer switch or a panel interlock kit with a properly rated inlet box, installed by a licensed electrician. Never backfeed through a dryer outlet or a double-male cord. Check whether your generator has a bonded neutral and whether your transfer equipment switches the neutral, because that determines grounding requirements.
FAQ
Is a tri-fuel generator the same as a standby generator?
No. A standby generator is permanently installed with an automatic transfer switch and starts on its own. A tri-fuel portable must be rolled out, connected and started manually. The trade-off is cost: a portable plus gas stub-out and interlock is typically a fraction of a standby installation.
Can I run a tri-fuel generator on natural gas indefinitely?
Fuel supply will not run out, but the engine still needs oil changes, typically every 50 to 100 hours depending on the manual, and a cool-down check. Plan for oil and filter supplies if you expect multi-day runs.
Bottom line
A tri-fuel generator earns its premium only if you will actually connect it to natural gas through a properly installed outdoor stub-out. In that case, it gives near-unlimited run time at a modest output penalty, bridging the gap between a portable and a standby unit. Without natural gas at your home, a dual-fuel generator delivers the same flexibility for less money.
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