Why propane fixes the real failure mode
The commonest way a backup generator fails is not mechanical. It is that the machine sat for eleven months with gasoline in it, the fuel oxidized and left varnish in the carburetor jets, and it will not start on the one morning it is needed.
Propane does not do this. It is stored under pressure in a sealed cylinder, it does not oxidize, it does not absorb water, and it leaves no residue when it burns. A generator that has only ever run propane has a clean carburetor by default.
For a machine that runs a handful of hours a year, that single property outweighs most of the specification sheet. The fuel storage page covers what stabilized gasoline can and cannot do about the same problem.
What propane costs you
Three things, and being straight about them matters.
1. Output, by roughly 10%. Propane has lower energy density per unit of volume delivered to the cylinder, so every dual fuel machine publishes a lower propane figure.
| Machine | Gasoline running | Propane running |
|---|
| Westinghouse WGen9500DF | 9,500 W | 8,500 W |
|---|
| DuroMax XP13000HXT | 10,500 W | 9,500 W |
|---|
| Westinghouse WGen7500DF | 7,500 W | 6,750 W |
|---|
| Champion 100165 | 7,500 W | 6,750 W |
|---|
2. Run time per container. A 20 lb barbecue cylinder is the standard unit, and on a mid-size machine under load it is a matter of hours rather than a day. Plan on several cylinders for a multi-day outage, or a larger tank.
3. Cold-weather behavior. Propane vaporizes less readily as temperature drops, and a cylinder drawn hard in deep cold can frost and lose pressure. Where winters are severe this is a real consideration — the cold weather page covers it properly.
Cylinders, tanks and lines
Three supply arrangements, and they suit very different situations.
20 lb cylinders. The barbecue tank. Cheap, exchangeable almost anywhere, and the right answer for occasional use and for RVs. The drawback is how often you swap them under sustained load.
A 100 lb cylinder or a residential tank. If the property already has propane for heating or cooking, tapping that supply removes the swapping problem entirely and is usually the best arrangement available. It needs a regulator and a fitting done properly.
Natural gas. Not propane, but the same family of argument taken further: a supply line that never runs out and needs no storage. The natural gas versus propane page works through the trade for standby units, and most of it applies here.
Propane storage is easier and still not free
Propane cylinders store outdoors, upright, away from ignition sources and never inside a house or an attached garage. They do not degrade, so buying them out of season is genuinely a store of readiness rather than a thing that expires.
Compare that with gasoline, where quantity limits, stabilizer and rotation all apply. The fuel storage page covers the gasoline side.
Dual fuel is almost always the right buy
There is very little market for propane-only portable generators, and that is rational. A dual fuel machine costs slightly more than a gasoline-only equivalent and gives you both failure modes covered: run propane by default for storage reasons, and burn gasoline when propane runs out or the cold reduces its output.
The dual fuel roundup covers the switching mechanics, and the tri-fuel page covers adding natural gas to that.
The short version
- Propane never goes stale. That fixes the commonest real-world failure.
- Expect about 10% less output. Size against the propane figure.
- Count cylinders, not just watts. A 20 lb tank is hours, not days.
- Buy dual fuel. The premium over gasoline-only is small and it covers both problems.
