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A propane generator for house backup solves the most annoying problem with gasoline models: fuel that goes bad. Propane stores indefinitely, so the tank you fill this year will still start the generator five years from now. That single property changes how backup power works for a house, and it is why propane (usually as half of a dual-fuel unit) is our default recommendation for portable backup. Here is what else matters.
Why propane beats gasoline for standby duty
Gasoline degrades within three to six months unless stabilized, absorbs water, and is miserable to source during a regional outage - every gas station within reach is either queued or dark. A 100-pound propane tank on your property is immune to all three problems. Engines also tolerate propane well: no carburetor gumming during long storage, cleaner combustion, and no ethanol damage.
The tradeoff is honest: propane carries less energy per gallon, so a dual-fuel generator produces roughly 10 percent less power on propane than on gasoline. A unit rated 9,500 starting watts on gasoline typically delivers around 8,500 on propane. That gap rarely changes which size class you need, but run the generator size calculator with the propane number, not the gasoline one.
Whole-house propane standby units
Every major standby line - Generac Guardian, Kohler, Briggs & Stratton - runs on natural gas or propane from the factory. On propane they need a tank, and tank sizing is the real decision: a 500-gallon tank runs a 22kW unit at half load for roughly a week. Homes without natural gas service (much of rural America) are the natural fit, and installers typically purchase or lease the tank as part of the project. Our cost guide prices this out.
For the portable path, the models we reference in the comparison table are dual-fuel: Westinghouse WGen7500DF, DuroMax XP5500EH, and Champion's 7,500W-class dual-fuel units are the usual suspects in the $800-$1,500 range.
Tank sizing quick reference
| Tank | Usable propane | Runs a 7.5kW portable at half load |
|---|---|---|
| 20 lb (grill tank) | ~4.6 gal | Roughly 10-12 hours |
| 100 lb | ~23.6 gal | 2-3 days |
| 100 gal | ~80 gal | About a week |
| 500 gal (standby) | ~400 gal | Weeks, unit-dependent |
Grill tanks work in a pinch but chain two together with a proper manifold; a single 20-pound tank will have you refilling every half day of an outage.
Safety notes that are not optional
Propane systems need proper ventilation and leak-checked connections. Never store tanks indoors or in a garage. Portable generators themselves stay at least 15 feet from the house regardless of fuel; carbon monoxide does not care which tank you picked. If you are wiring the generator into your panel, that legally requires a transfer switch.
FAQ
Can I convert my gasoline generator to propane?
Aftermarket tri-fuel kits exist for many common models and work well when professionally installed. They cost $150-$400 and slightly reduce gasoline-rated output. Check that your specific engine has a supported kit.
Does propane go bad?
No. Propane is stable indefinitely - the tank itself needs recertification every 10-12 years for refilling, but the fuel does not degrade.
Is a propane generator cheaper to run?
Per hour at equal output, propane and gasoline usually land within 10-20 percent of each other with normal price swings. Propane wins on storage life and availability during outages, not on fuel cost.
What size propane generator do I need for my house?
The same answer as any fuel: your appliance list decides. Run it through the calculator, then buy the tank that feeds that size for your target outage duration.
