Why tank size matters for generators

Unlike a natural gas generator that draws from the utility line, a propane generator is limited by how much fuel is stored on-site. How long it can run during an extended outage depends directly on two things: how fast the generator burns fuel (proportional to size and actual load) and how much propane is available in the tank.

Common propane tank sizes and their generator run-time

A 250-gallon tank holds roughly 200 gallons of usable propane — tanks are filled to 80% capacity as a standard safety practice. A 22 kW generator running at 50% load burns approximately 2.0–2.5 gallons per hour. At that rate, 200 usable gallons supports roughly 80–100 hours of operation, or about 3–4 days of continuous running.

A 500-gallon tank (about 400 usable gallons) doubles that figure to roughly 160–200 hours at the same load — approaching 7–8 days continuous. A 1,000-gallon tank provides enough propane for extended multi-week outages without a refill, though this tank size comes with higher upfront cost and requires more installation space.

Recommended tank sizes by generator capacity

For a 7–10 kW essentials-only generator: a 250-gallon tank typically provides adequate run time for most residential outage durations. For a 14–20 kW whole-home setup: a 500-gallon tank is a more comfortable fit if you want several days of run time without worrying about refills. For a 22–26 kW unit sized for full whole-home coverage including HVAC: a 500-gallon tank is a reasonable minimum; a 1,000-gallon tank provides meaningfully more cushion for extended or severe-weather outages.

Leasing vs. buying a propane tank

Many propane suppliers offer tank leases tied to a fuel delivery contract, which keeps upfront cost lower. Leased tanks require you to purchase fuel from the lessor — a consideration if other suppliers offer better pricing. Purchased tanks allow deliveries from any supplier, which provides more pricing flexibility over time.

Confirm with your installer whether the installation quote includes a tank purchase, a lease arrangement, or neither. Tank sourcing is sometimes handled separately from the generator installation itself.