Home / Generators

Propane vs gas generator: what changes when you switch fuel

By the Plain Prepper editors. Updated 2026-10-15.

We research products from makers' specs, manuals and safety agencies; we do not run hands-on tests. Links to Amazon may earn us a commission at no cost to you. How this works.

Quick answer

On the same dual-fuel generator, propane gives about 10% less power than gasoline. Westinghouse rates its WGen9500DFc at 9,500 running watts on gas and 8,500 on propane, and its iGen2800DFc at 2,200 and 1,980. EIA lists propane at 91,452 Btu per gallon versus 120,214 for gasoline, about 24% less energy per gallon. Propane's advantage is storage: it stays in sealed cylinders outdoors, while gasoline needs approved cans kept outside living areas. Either fuel makes deadly carbon monoxide; run generators 20 feet from the house.

Output: propane runs about 10% lower

Dual-fuel generators list separate ratings for each fuel. Westinghouse's numbers:

Model	Gasoline running / peak	Propane running / peak	Propane vs gas (running)
WGen9500DFc EFI	9,500 / 12,500 W	8,500 / 11,200 W	About 89%
iGen2800DFc inverter	2,200 / 2,800 W	1,980 / 2,520 W	90%

Size for the propane rating if you plan to run on propane. A load list that fits 9,500 W on gas may overload the same machine at 8,500 W on propane.

Energy per gallon and runtime

The U.S. Energy Information Administration lists heat content per gallon:

• Gasoline: 120,214 Btu
• Propane: 91,452 Btu

That is about 24% less energy per gallon for propane (91,452 / 120,214 = 0.76), so a generator burns more gallons of propane than gasoline for the same work.

Westinghouse's runtime figures for the WGen9500DFc show the same pattern: 10 hours at 50% load on its 6.6-gallon gas tank and 8.75 hours at 50% load on propane. The propane figure does not state the cylinder size, so check the manual before planning around it. Compare runtimes at the same load percentage only.

Worked example: the same machine on each fuel

Take the WGen9500DFc and a planned load of 8,000 running watts on 240 V circuits:

• On gasoline: 8,000 of 9,500 W is about 84% of the rating, leaving headroom for motor starts within the 12,500 W peak.
• On propane: 8,000 of 8,500 W is about 94% of the rating, with less room for a refrigerator or pump to start.

Westinghouse's amp ratings make the same point: 39.6 A running on gasoline versus 35.4 A on propane.

Fuel volume shifts too. A full 6.6-gallon gas tank holds about 793,000 Btu (6.6 x 120,214). Matching that energy with propane takes about 8.7 gallons (793,412 / 91,452), before differences in engine efficiency on each fuel. In practice, plan more propane by volume than gasoline for the same hours of runtime.

Storage: where propane wins

For outage preparedness, fuel storage often decides the question.

• Propane stays sealed in its cylinder. The propane industry's safety booklet says to keep cylinders outside, upright, away from heat, and never in a basement, garage, shed or tent, and to use only cylinders with an overfill prevention device.
• Gasoline must be kept in containers made and labeled for fuel, stored outside living areas, according to NFPA's generator safety tips.

Both fuels need care. A dual-fuel machine lets you use whichever fuel you can get after a storm.

Which to choose

• Choose gasoline-first if you need every watt the generator can make and can rotate stored fuel.
• Choose propane-first if you want sealed fuel storage and are sizing loads to the lower propane rating.
• Choose dual fuel for flexibility. Westinghouse includes a propane regulator and hose with the WGen9500DFc.

Quieter inverter models trade raw output for lower noise: Westinghouse lists 52 dBA for the iGen2800DFc versus 74 dBA for the WGen9500DFc.

Safety does not depend on the fuel

NFPA's tips apply to both fuels:

• Portable generator exhaust is toxic. Run it outdoors at least 20 feet from doors, windows and vents, with exhaust pointed away from the building.
• Never run it in an attached garage, even with the door open.
• Install CO alarms in the home.
• Turn the generator off and let it cool before refueling.
• Use heavy-duty outdoor cords, or have a qualified electrician install a transfer switch to connect to house wiring.

Both Westinghouse models listed here include a CO sensor.

What to look for when you buy

Questions people ask

Do generators make less power on propane?

Yes, about 10% less on the Westinghouse dual-fuel models here: 8,500 vs 9,500 running watts, and 1,980 vs 2,200.

Does propane or gas last longer in a generator?

Per gallon, gasoline holds more energy: EIA lists 120,214 Btu vs 91,452 for propane. Westinghouse's WGen9500DFc runs 10 hours on gas and 8.75 on propane at 50% load.

Is propane safer to store than gasoline?

Propane is sealed in cylinders kept outdoors; gasoline needs labeled fuel containers stored outside living areas. Both are flammable and both make carbon monoxide when burned.

Can I run a propane generator indoors?

No. NFPA says any portable generator must run outdoors at least 20 feet from doors, windows and vents.

Sources

• WGen9500DFc EFI dual fuel generator: specs, Westinghouse Outdoor Power
• iGen2800DFc dual fuel inverter generator, Westinghouse Outdoor Power
• British thermal units: heat content of fuels, U.S. Energy Information Administration
• Generator safety tips, National Fire Protection Association
• Propane safety booklet PRC-101063D: portable cylinders, Propane Education and Research Council

Sources checked 2026-10-15.