How Long Does a 20 lb Propane Tank Last on a Generator?

About 10 to 12 hours at 1,500 W on a mid-size dual fuel inverter generator, and about 20 hours at 800 W. Large open-frame generators use a tank in about 6 to 7 hours even at light loads.

About 6 to 7 grill tanks at 1,500 W, or about 4 at 800 W, on a mid-size inverter generator. Running the generator in shifts, such as four hours on and four off, cuts that roughly in half.

Yes, by volume. A gallon of propane holds about 70 percent of the energy of a gallon of gasoline, so a generator burns about 1.4 gallons of propane for every gallon of gas. Propane stores for years without going stale, which gas does not.

Yes. A 100 lb tank holds about 23.6 gallons, about five grill tanks, and runs a 4,500 W class inverter about 2.5 days at 1,500 W. Most 100 lb tanks have a POL valve, so you need a POL to QCC1 adapter or a hose made for them.

About 24 hours at 1,500 W on a 4,500 W class inverter generator. A 40 lb tank holds about 9.4 gallons, twice a grill tank, and uses the same QCC1 hose. At 800 W expect roughly twice that.

Use a gauge, or weigh the tank and subtract the tare weight stamped on the collar as TW. Whatever is left over is the propane, out of 20 lb when full. At 1,500 W on a mid-size inverter one tank lasts about 11 hours, so each pound is worth roughly half an hour.

Gas is usually cheaper. A 20 lb tank holds about 4.6 gallons of propane, which equals about 3.3 gallons of gasoline (4.6 / 1.4). At $22 a tank that is about $6.70 per gallon of gas equivalent, roughly twice the cost of gas at $3.20. You pay the extra for fuel that keeps for years.

Some drop is normal, since every maker rates output about 10 percent lower on propane. Beyond that, the usual causes are a nearly empty tank, a tank too cold to vaporize propane fast enough, or the flow-limiting safety in the QCC1 hose fitting tripping because the valve was opened quickly. Close the valve, reconnect, open it slowly, and move to a fuller or bigger tank at heavy loads.

Outdoors, upright, in a ventilated spot away from the generator exhaust and out of direct sun. Never inside the house or an attached garage. The NFPA 58 fire code limits propane cylinders kept inside a home to small 1 lb cylinders.

The propane itself does not go stale, which is why it is the better fuel to store for outages. The tank does have a limit: a 20 lb DOT cylinder must be requalified 12 years after the manufacture date stamped on the collar before it can be refilled. Exchange services swap out-of-date tanks for you.