How much propane does a standby generator use?
Short answer: A 22 kW standby generator burns about 2.5 gallons of propane an hour at half load and about 3.7 at full load, roughly 60–90 gallons a day. A 500-gallon tank filled to 80% runs it about 4½–6½ days.
Propane use by generator size
Gallons per hour, estimated with our fuel calculator (propane at 91,452 BTU/gal, EIA). Real figures for your model are on its spec sheet, usually at ½ and full load.
| Generator | 25% load | 50% load | 100% load | Gallons/day at 50% |
|---|---|---|---|---|
| 14 kW | 0.96 | 1.58 | 2.37 | 38 |
| 18 kW | 1.23 | 2.04 | 3.05 | 49 |
| 22 kW | 1.50 | 2.49 | 3.73 | 60 |
| 26 kW | 1.78 | 2.94 | 4.41 | 71 |
How long tanks last on a 22 kW generator
| Propane supply | Usable gallons | At 50% load | At 100% load |
|---|---|---|---|
| 20 lb cylinder (grill tank) | 4.7 | 2 h | 1 h |
| 30 lb cylinder | 7.1 | 3 h | 2 h |
| 100 lb cylinder | 23.6 | 9 h | 6 h |
| 250 gal tank (filled to 80%) | 200.0 | 80 h | 54 h |
| 500 gal tank (filled to 80%) | 400.0 | 161 h | 107 h |
| 1,000 gal tank (filled to 80%) | 800.0 | 322 h | 214 h |
Tanks are filled to 80% to leave room for the liquid to expand. A 20 lb grill cylinder lasts under two hours on a 22 kW standby, which is why standby generators run on a large tank or natural gas.
Your real load is lower than you think
Standby generators sit at 25–50% load most of the time: the fridge cycles, the AC cycles, and nobody runs the dryer during an outage. But at light load, an engine is inefficient — it burns about 40% of its full-load fuel at 25% load. That's why weekly exercise cycles (often 5–12 minutes) add up too: about a gallon or two a month.
Natural gas instead?
If you have a natural gas service, a standby generator on it never runs out — but the gas meter and service line must be sized for it. A 22 kW unit at full load needs roughly 329 cubic feet per hour, on top of your furnace and water heater. Your gas utility checks this before installation.