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.
In short
- Availability decides this more often than preference does. Where a gas main reaches the house, natural gas usually wins; where it does not, propane is the answer.
- The same unit makes less power on natural gas. Propane carries far more energy per unit of volume — roughly 2,500 Btu per cubic foot — which is why a derate appears on nearly every spec sheet.
- Natural gas trades power for continuity: nothing to refill, no tank to site, and a lower running cost where both fuels are offered.
- Propane trades continuity for power: full rated output, but a finite runtime that depends on tank size and refills.
Read this if
- Both fuels are physically available and you have to choose.
- A quote assumes one fuel and you want to know what that assumption costs you.
- You are sizing a unit and need to know which rating to size from.
Skip it if
- No gas main reaches your property. The decision is made for you — propane — and the sizing question is the live one instead.
- You want a running-cost figure for your address. Fuel prices are local and move; this page compares the fuels, not today's rates.
What to confirm for your own home
- The rated output of the specific model you are quoted, on the fuel you will actually run — not the headline kW.
- That your gas utility has reviewed whether the existing meter and service can carry the added load.
- For propane: the tank size being proposed, who owns it, and the resulting runtime at your expected load.
What this page does not do
It does not price fuel for your address, and it does not tell you your generator needs a larger gas meter. A generator-specific meter-upsizing mandate could not be confirmed from any authoritative utility source — the claim circulates on contractor blogs — so we frame it as a capacity review to request, not a requirement to assume.
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.
Four ways the fuel decision goes wrong
Assuming the advertised kW is what you get on natural gas.
InsteadNatural gas carries less energy per cubic foot, so the same unit makes less power on it — that is the derate on nearly every spec sheet. Size from the rating for the fuel you will actually run, using the sizing guide.
Choosing propane for the extra output without costing the runtime.
InsteadPropane delivers full rated power, but the tank is finite. Ask what tank size is proposed and what runtime that gives at your expected load — an outage that outlasts the tank is a generator that stopped.
Budgeting for a larger gas meter because a contractor said one is required.
InsteadAsk the gas utility for a service and meter capacity review. A generator-specific upsizing mandate could not be confirmed from any authoritative utility source — it appears on contractor blogs, not in utility rules. Treat it as a question, not a given.
Comparing running costs using a national fuel price.
InsteadBoth fuels are priced locally and both move. The durable comparison is energy per unit of volume and how the fuel is supplied; the dollar figure has to come from your own utility and propane supplier.
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. Because the natural-gas derate changes the kW you actually get, settle the fuel before you settle the size — the sizing guide works from the rating on the fuel you will actually run. Then 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 read every request against what installers are actually covering here, and tell you what that coverage looks like — and we are not a national call center.
Prefer to send the full picture up front? Send a Generator Project Brief — coverage objective, fuel, priority loads, and timeline, so the installer's first call starts at the proposal. “Not sure” is an accepted answer throughout.