Fuel type and generator output

Why ratings differ

The engine must convert the supplied fuel into enough mechanical power to support electrical generation. Fuel properties, engine design, and the fuel-delivery system influence that capability. The resulting ratings are properties of the complete product; fuel energy content alone cannot predict a universal output reduction. [2]

Fuel must also arrive at the required pressure and flow. A published rating assumes the specified supply and operating conditions. Inadequate delivery should be investigated as a supply problem rather than accepted as the normal capacity of that fuel. Manufacturer altitude and temperature corrections may further affect the available rating. [2] [3]

A manufacturer example

Champion’s model 201176 provides a useful example of separate ratings for one product. Its published running capacities are 7,250 W on gasoline, 6,525 W on propane, and 5,875 W on natural gas. It lists 9,000 starting watts for all three fuels. These specifications do not establish the same relationship for another model. [1]

Read the whole specification

Keep running capacity separate from a short-term starting rating. Also distinguish real power in kW from apparent power in kVA and note the rated voltage and phase. A connection or breaker’s ampere label is not an independent promise of generator output. [1] [2]

Fuel consumption and runtime answer different questions. Consumption describes fuel used at a stated load, while runtime also depends on usable fuel inventory and operating assumptions. A longer advertised runtime does not demonstrate a higher output rating.

For a useful comparison, record the fuel you intend to use, its running rating, any documented starting performance, and the site conditions. Recheck the load plan if the fuel changes. For an installed generator, confirm these inputs with the installer and the current specification sheet for the exact configuration.