Fuel Choice
Natural Gas vs. Propane for a Standby Generator: How to Choose
The fuel decision changes your generator's power output, how long it can run, and what it costs to run. Here is how natural gas and propane actually compare — sourced to manufacturer specs and U.S. energy data.
Power Output: The Same Unit Makes Less on Natural Gas
On the same generator, natural gas produces less power than propane. The Kohler 14RCA, for example, is rated 14 kW on propane vs. 12 kW on natural gas. Generac's 22–28kW line likewise runs a few percent lower on natural gas than on propane.
Confirm the exact rating you're quoted
Generac's published natural-gas rating for its 26 kW class appears differently across its own spec sheets — anywhere from 22.5 kW to 24 kWdepending on the document and model number. Confirm the exact natural-gas rating of the specific model you're quoted before you sign.
Why Natural Gas Produces Less
It comes down to energy density. Propane carries far more energy per unit of volume than natural gas — roughly 2,500 Btu per cubic foot of propane vapor versus about 1,036 Btu per cubic foot of natural gas, per the U.S. Energy Information Administration. Feed an engine a fuel with less energy per cubic foot and it makes less power. That is the general reason behind the natural-gas derate you see on nearly every spec sheet.
Supply & Runtime
Power output is only half the decision. The bigger practical difference is where the fuel comes from and how long it lasts.
| Dimension | Natural gas | Propane |
|---|---|---|
| Supply | Continuous municipal gas line | Finite on-site tank |
| Refueling | None — piped in | Depletes; needs periodic refills |
| Runtime | Runs as long as the gas main holds | Limited by tank size; ends when the tank runs dry |
Which Fuel for Your Home?
Start with what's available at your address. If the home has no natural-gas service, propane is the option — Kohler states this directly, and tank sizing and placement are coordinated with your dealer.
If natural gas is available at the property, it is the simpler choice: a continuous supply with no tank to monitor or refill.
Operating Cost
Where both fuels are available, propane generally costs more per unit of energy than natural gas. This is a durable, structural difference, not a temporary market swing: propane is trucked in and carries a delivery markup, while natural gas is a pipeline utility commodity.
We don't publish a $/hour or per-unit price here — current energy prices vary by region and season. For today's numbers, the U.S. Energy Information Administration (EIA) is the source to check; for what an install itself costs, see our cost guide.
Cold Weather
In freezing climates, manufacturers recommend cold-weather accessories (a battery warmer, oil/crankcase heater, and the like). Kohler calls for these below 32°F.
We'll stop where the documentation stops: there is a common claim that propane “stops vaporizing” at some specific temperature, but we found no manufacturer figure for that, so we won't put a number on it. The sourced, honest guidance is the cold-weather accessory recommendation above — which applies to the generator regardless of fuel.
The Bottom Line
If natural gas is available at your home, it usually wins: continuous supply, nothing to refill, and a lower running cost where both fuels are offered. You give up a few percent of rated power to the natural-gas derate.
If there's no gas main, propane is the answer — and it delivers the unit's full rated power. The trade-offs are a higher running cost and a finite runtime that depends on tank size and refills. Either way, confirm the exact fuel rating of the specific model you're quoted, and see the Generac vs. Kohler comparison and the maintenance guide before you commit.
Sources & methodology
Figures on this page are sourced to manufacturer specification sheets and to the U.S. Energy Information Administration / Department of Energy, retrieved June 2026. Where a manufacturer's own documents disagree (Generac's 26 kW natural-gas rating), we say so rather than pick one. Where a common claim isn't documented (a specific propane cold-weather vaporization temperature), we leave it out rather than guess. Energy prices change; we point to the EIA for current numbers instead of dating them here.
Not sure which fuel fits your home?
Tell us about your home. We connect you with established local installers — not a national call center.