The output ladder, with real numbers
Most fuel comparisons in this category are qualitative. DuroMax publishes all three ratings for the XP13000HXT, which lets the argument be made properly:
| Fuel | Running watts | Starting watts | Against gasoline |
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| Gasoline | 10,500 | 13,000 | Reference |
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| Propane | 9,500 | 12,000 | About 10% less |
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| Natural gas | 8,500 | 10,000 | About 19% less |
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DuroMax's published ratings for the XP13000HXT. Percentages are calculated from those figures. The pattern holds across the category — Generac publishes 24kW on propane and 21kW on natural gas for the same standby unit — because it follows from the energy density of each fuel rather than from any manufacturer's design choice.
The practical instruction that falls out of this: size against the fuel you will actually run. A machine marketed as 13,000 watts is an 8,500-watt machine on the gas main, and if your calculation landed on 9,000W you have just under-bought.
Why natural gas is worth the third connection
The output penalty is the largest of the three fuels, and the advantage is larger still: it does not run out.
A gasoline machine is limited by what is in your cans. A propane machine is limited by what is in the tank. A machine on the gas main runs for as long as the outage lasts, with nobody carrying anything.
In a multi-day outage that is worth far more than 19% of output, because the thing that ends most generator runs is fuel rather than capacity.
The catches are real and worth naming:
- Connecting to the gas main is plumbing work. A permanent connection needs a licensed installer, a shut-off valve and usually a permit. A quick-connect fitting is the common arrangement.
- Pipe sizing may need upgrading. A generator is a large gas appliance, and the existing run may not deliver enough at the required pressure.
- The main can be interrupted by the same earthquakes and major storms that take the power out. It is more reliable than the grid, not infallible.
The fuel comparison works through the same trade at standby scale.
Is tri-fuel worth it over dual fuel?
The answer is unusually clean, and it is a yes-or-no question about your property rather than a judgment call.
Yes, if you have a natural gas main at the house. The third fuel is unlimited runtime, and that is the single most valuable property a backup fuel can have. It is worth the price premium and the installation.
No, if you do not. Without a main, the natural gas capability is a fitting you will never connect, and you have bought a dual-fuel machine at a higher price. Buy dual fuel instead and put the difference toward fuel storage or a battery.
How the three fuels compare on everything else
| Gasoline | Propane | Natural gas |
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| Runtime limit | What is in the cans | What is in the tank | None |
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| Goes stale | Yes — months | No | Not applicable |
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| Availability in an outage | Poor — station pumps are electric | Good if already stored | Excellent, unless the main is cut |
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| Cold weather | Fine | Vaporizes more slowly in severe cold | Unaffected |
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| Storage on site | Cans, rotated, legally limited | Cylinders or a tank | Nothing to store |
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| Setup cost | None | Tank or cylinders | Plumbing and possibly a permit |
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Fuel prices are deliberately absent — they vary too much by region and season for a comparison to be useful. The dual-fuel page works costs at dated EIA prices for the two fuels where a national figure exists.
How to actually run one
The strategy that gets the most from a tri-fuel machine is not to pick a fuel — it is to use each one for what it is good at.
- Natural gas as the default. Unlimited runtime, nothing to carry, nothing to store. Accept the output penalty and size for it.
- Propane as the reserve. For the case where the main is cut, and for the higher output if you ever need it. It never goes stale, so a cylinder bought today still works in five years.
- Gasoline as the emergency option only, and only if you have a reason to keep it. Otherwise skip it — running the gasoline system dry and never using it removes the entire stale-fuel maintenance problem.
- Exercise it monthly on gas or propane, which keeps the engine healthy with no fuel-storage consequences at all.
That arrangement gives you a machine that always starts, never needs fuel rotation, and has a fallback for the one failure its primary fuel can have.
The safety rules do not change
Every fuel here produces carbon monoxide when burned. Outdoors, at least twenty feet from windows, doors and attached garages, exhaust pointed away, and a working alarm on every level of the house.
The one addition specific to gaseous fuel: a leak at the connection is a different hazard from a gasoline spill, and it is why the gas connection is licensed work rather than a job for a fitting from a hardware store. The full safety guidance covers the rest.
