Propane vs Gasoline for Generators: Cost and Convenience Compared

Most dual-fuel generator owners pick a favorite fuel and rarely use the other. The choice usually comes down to two practical questions: which one costs less per hour of power, and which one is less hassle when you are tired, it is dark, and the outage is on day three. The answers depend on how you buy propane, how cold it gets, and how long your generator sits between uses. This comparison puts real numbers on the cost side and walks through the day-to-day convenience trade-offs so you can decide which fuel should be your primary and which your backup.

Cost per kilowatt-hour: the fair comparison

Comparing price per gallon is misleading, because a gallon of propane holds roughly 25 percent less energy than a gallon of gasoline, and dual-fuel generators often make slightly less power on propane. The fair comparison is fuel cost per kilowatt-hour of electricity produced. The figures below are illustrative; plug in your local prices.

*Assumes a mid-size portable at roughly half load; actual efficiency varies by model and load.

The pattern is clear: exchange cylinders are the most expensive way to run a generator, refills are better, and bulk propane can approach or match gasoline. Note that many exchange cylinders are filled to about 15 lb rather than 20 lb, so you get less fuel than you might assume.

Runtime per container

Convenience depends a lot on how often you swap containers.

• 5 gallon gas can: at 0.5 gallons per hour, about 10 hours.
• 20 lb propane cylinder (about 4.6 gallons): at 0.65 gallons per hour of propane for a similar load, about 7 hours.
• 100 lb cylinder (about 23.6 gallons): roughly 36 hours at the same rate, though it weighs about 170 pounds full.

Some owners connect a larger cylinder through an appropriately rated hose so the generator runs for days without a swap.

Convenience factors

Storage life

Propane wins decisively. It does not go stale, so cylinders filled years ago still work. Gasoline needs stabilizer and rotation every few months. For a generator that might sit for a year between outages, this alone makes propane attractive.

Engine health

Propane burns cleanly and does not varnish the carburetor. Many no-start problems come from gasoline left in the carburetor. Owners who run primarily on propane often report fewer maintenance headaches.

Refueling

Swapping a propane cylinder involves closing the valve, disconnecting and reconnecting the regulator, and checking for leaks. It avoids pouring fuel near a hot engine, though most manuals still advise shutting down for the swap. Gasoline requires the engine to cool before pouring to avoid igniting spills.

Cold weather

Gasoline wins in deep cold. Propane vaporizes more slowly as temperatures drop, and a small cylinder feeding a hungry engine can frost up and lose pressure. Larger cylinders handle cold better because they have more surface area.

Availability during outages

Gas stations without power cannot pump. Propane exchanges at grocery and hardware stores may sell out before a storm. Bulk propane delivery keeps working if roads are open. Stocking up in advance matters for both.

Storage rules and safety

Propane cylinders must be stored upright outdoors, never in a garage, basement or house. Gasoline can be kept in approved cans in a garage, within local limits. Both fuels produce carbon monoxide when burned, so the generator stays outdoors, at least 20 feet from the house, exhaust pointed away from openings, never in a garage or on a porch.

A practical dual-fuel strategy

Keep three to four propane cylinders filled as your long-term reserve, since they never go bad. Keep a smaller amount of stabilized gasoline for cold snaps and for extra power when you need the full rating. Exercise the generator monthly on both fuels. When an outage arrives, run on gasoline first while it is fresh, then switch to propane.

FAQ

Why does my generator produce less power on propane?

Propane contains less energy per unit volume, so the engine produces less power per intake stroke. Dual-fuel generators commonly list a propane rating about 5 to 10 percent lower than their gasoline rating.

Is it cheaper to refill or exchange propane cylinders?

Refilling is usually cheaper, because you pay only for the gallons pumped and the cylinder is filled completely. Exchanges trade convenience for a higher price per gallon.

Bottom line

Gasoline is usually cheaper per kilowatt-hour than exchanged propane cylinders and performs better in extreme cold. Propane stores indefinitely, keeps engines clean and can match gasoline on cost when bought in bulk. For most dual-fuel owners, propane makes the best long-term reserve and gasoline the best short-term fuel.