Fuel choice · buying guide
The better fuel depends on the property: utility-gas availability and capacity, propane storage, winter conditions, outage duration, the exact generator's fuel-specific output, and local fuel prices.
Direct answer
Natural gas is often attractive when a capable utility service already exists because you do not have to manage a stored fuel reserve. Propane can make sense where natural gas is unavailable or where an on-site reserve is preferred. But a propane system must be sized for both runtime and cold-weather vaporization, while a natural-gas system still needs enough meter and piping capacity for the generator at load.
Side-by-side
| Factor | Natural gas | Propane (LP) |
|---|---|---|
| Fuel supply | Utility pipeline supply can support long outages when gas service remains available. | Stored on-site, so outage runtime depends on usable tank capacity and refill access. |
| Installation | Existing meter, regulator and piping must support the generator's required gas flow; upgrades may be needed. | Requires appropriately sized tank/storage, regulator setup and fuel piping. |
| Cold weather | No tank-vaporization constraint, but regulators, vents and the generator itself still need winter-ready operation. | Low temperatures can reduce propane vaporization capacity, especially with small or low tanks and high generator demand. |
| Generator output | Some dual-fuel standby models are rated for less output on natural gas than on propane. | Some dual-fuel models publish a higher kW rating on LP. Always compare the exact model's fuel-specific rating. |
| Fuel on property | No large on-site fuel tank when utility gas is available. | Provides a private stored fuel reserve but requires space, tank ownership/lease decisions and refill planning. |
| Price | Operating cost depends on local utility rates and generator fuel-consumption curves. | Operating cost depends on delivered propane price, tank arrangement and fuel consumption. There is no universal cheapest fuel. |
Having a gas meter does not prove the service can support a standby generator. Generator demand is added to the home's other gas loads, and long or undersized piping can create pressure problems. A qualified installer or gas utility should verify the available capacity.
Tank capacity affects runtime, but cold-weather vaporization also matters. A tank that appears large enough by gallons can still struggle to vaporize fuel fast enough for a high-demand generator in very low temperatures.
Cold weather increases the importance of propane storage design, regulator protection, generator winter accessories, battery condition and snow/ice clearance. That is why a Vermont installation can need different planning than the same generator in a mild climate.
Fuel-specific output
Manufacturers often publish separate natural-gas and propane ratings. Some models produce less power on natural gas. Compare the specification sheet using the fuel you will actually install before choosing generator size or deciding what loads it can support.
Decision checklist
Common homeowner questions
There is no national answer. Use your local utility rate or delivered propane price together with the exact generator's fuel-consumption data at realistic loads.
Not literally. It can avoid the finite on-site storage limit of propane, but utility gas service can still be interrupted and the generator still requires maintenance during extended operation.
Tank sizing depends on generator fuel consumption, desired runtime, other propane appliances, refill strategy and cold-weather vaporization. Do not size only by a generic days-of-runtime chart.
Many standby models are field-configurable, but conversion/setup is model-specific and may require fuel-system adjustments or parts. Use the exact installation/service documentation.
It gives you a known on-site reserve, which can be valuable. Its tradeoff is finite storage plus refill logistics and cold-weather vaporization constraints.
Yes when the model's published output differs by fuel. Size the system from the rating for the fuel you will actually use.
Next decision
Fuel rating, load profile, transfer equipment, placement and piping/electrical scope are connected decisions—not separate shopping steps.