Why the kW rating doesn't tell the whole story

A 22 kW generator doesn't always burn propane at its maximum rated rate — it burns fuel in proportion to the actual electrical load being drawn from it. A generator running a refrigerator, some lights, and a sump pump might be at 20–30% of rated capacity; the same generator running central air and the kitchen simultaneously might be at 60–80%. Actual consumption tracks load, not nameplate capacity — which is why correct sizing affects operating cost as well as coverage.

Typical propane consumption by generator size

At 50% load — a reasonable estimate for typical residential use — approximate consumption rates are: 7 kW generator: 0.6–1.0 gallons per hour. 14 kW: 1.3–1.9 gallons per hour. 20 kW: 1.8–2.5 gallons per hour. 22 kW: 2.0–2.8 gallons per hour. 26 kW: 2.4–3.5 gallons per hour.

At 25% load, consumption drops by roughly 30–40% from the 50% figures. At full load (100%), consumption rises to roughly 1.5–2x the 50% rate. Running central air conditioning in summer heat is the single biggest load driver in most homes.

Run-time calculations

To estimate run time, divide the usable gallons in your tank by your expected consumption rate. A 500-gallon tank holds about 400 usable gallons at standard 80% fill. A 22 kW generator at 50% load consuming about 2.5 gallons per hour would run approximately 160 hours — about 6–7 days — on a full 500-gallon tank.

If you plan to run central air through a summer outage, use 70–75% load in your estimate. If running essentials only, 30–40% load is a reasonable lower bound.

How to use consumption estimates for outage planning

Before a storm season, confirm your tank is at or near 100% fill rather than 50%. During a multi-day outage, reducing unnecessary loads — turning off electric water heaters, limiting electric oven use — extends run time meaningfully. If the outage extends beyond 3–4 days, contacting your propane supplier early to schedule a delivery is advisable. Wait times for propane delivery can extend significantly after major storms when regional demand spikes — which is a strong argument for sizing the tank generously up front.