How Much Propane Does a Generator Use Per Hour?
Estimate generator propane use from load and model ratings, then calculate portable-cylinder or bulk-tank runtime for an outage.
Published model ratings range from about 0.14 gallon per hour for a small inverter at 25% load to 0.7–1.2 gallons per hour for the portable generators in the examples below at 50% load. Selected 10–28 kW home standby models use roughly 1–4 gallons per hour, depending on size and load.
These are planning figures, not guaranteed burn rates. For the best estimate, use the propane-consumption table or runtime rating for your exact model at the closest expected load.
Propane use by generator size
These manufacturer examples show why wattage alone cannot determine fuel consumption.
| Propane running-watt rating | Test load | Published runtime on a 20-lb cylinder | Calculated propane use |
|---|---|---|---|
| 1,665W portable inverter | 25% | Up to 34 hours | 0.14 gal/hr |
| 5,850W portable | 50% | Up to 6.5 hours | 0.73 gal/hr |
| 7,200W portable | 50% | Up to 5 hours | 0.95 gal/hr |
| 13,000W portable | 50% | Up to 4 hours | 1.19 gal/hr |
The first three runtimes come from Champion ratings for its 2,500W inverter, 6,500W-class portable and 8,000W-class portable. The fourth comes from Westinghouse’s 13,000-running-watt propane model.
Gallons per hour were calculated using 4.2 pounds of propane per gallon, the approximate weight at 60°F listed in the Propane Technical Pocket Guide. Propane density changes slightly with temperature; see how much a gallon of propane weighs.
Home standby generator examples
Generac publishes these approximate liquid-propane rates for selected Guardian models:
| Standby rating | Half load | Full load |
|---|---|---|
| 10 kW | 0.97 gal/hr | 1.48 gal/hr |
| 14 kW | 1.81 gal/hr | 3.07 gal/hr |
| 18 kW | 1.70 gal/hr | 3.02 gal/hr |
| 22 kW | 2.53 gal/hr | 3.90 gal/hr |
| 26 kW | 2.06 gal/hr | 3.63 gal/hr |
The non-linear results are not errors: engine and alternator efficiency differs among designs. Generac calls the values approximate and directs owners to the model’s specification sheet or fuel-data decal for specific figures (Generac fuel-consumption tables).
Calculate how long your propane will last
Use:
Runtime in hours = usable propane gallons ÷ generator consumption in gallons per hour
A 20-lb cylinder filled to its rated propane capacity contains approximately:
20 lb ÷ 4.2 lb/gal = 4.76 gallons
If the generator burns 0.95 gallon per hour:
4.76 ÷ 0.95 = about 5 hours
Use the actual pounds of propane purchased—not merely the cylinder’s nominal size—because a cylinder exchange may contain less than 20 pounds. If needed, determine the remaining fuel by weight as explained in how to tell if a propane tank is empty.
For a bulk tank, multiply its water capacity by the gauge reading as a decimal. A 500-gallon tank reading 60% contains approximately 300 gallons. The gauge is an estimate, and a properly filled tank normally reads about 80%, not 100%, because expansion space is required. This 500-gallon conversion is also shown in Proulx Oil & Propane’s gauge guide.
At a 2-gallon-per-hour burn rate, an indicated 300-gallon supply provides a theoretical 150 hours. Plan for less if the same tank also feeds a furnace, water heater or other appliances.
What changes the burn rate
- Electrical load: More running watts generally require more fuel. Motors, pumps and air conditioners also have starting surges; size the generator for running load and startup demand using portable generator sizing and runtime.
- Generator design: Two generators with similar nameplate ratings can have different engines, alternators and efficiency curves.
- Operating mode: An inverter generator can reduce engine speed under light load, while many conventional units run at a fixed speed.
- Temperature and tank size: Propane must vaporize before the engine can use it. Cold lowers tank pressure and can restrict fuel delivery before the tank is empty, especially under high demand. There is no universal cutoff temperature because fuel composition and system requirements vary (Generac cold-weather guidance). Ask the propane supplier to verify tank and regulator capacity for a standby installation.
Plan an outage supply
- List the appliances that must run and total their running watts.
- Account for the largest starting surge.
- Find the manufacturer’s fuel rate at the nearest load percentage.
- Multiply gallons per hour by planned operating hours.
- Add fuel used by every other propane appliance and keep a practical reserve.
Reducing load and shutting the generator down when power is not needed can conserve fuel, but follow its manual for shutdown, cooling and maintenance.
For portable units, fuel planning never overrides carbon-monoxide precautions. The CPSC says to operate a portable generator outside only, at least 20 feet from the house, with exhaust directed away from the home and building entrances. Never run one in a garage, basement, shed, porch or carport. Maintain working CO alarms on every level and outside sleeping areas (CPSC generator guidance).