A full 30 lb tank contains about 639,000 BTUs, so your furnace would be able to run continuously for over 25 hours.

A 1,500 square foot home in a mild climate would require approximately 1.5 million BTUs of propane fuel for heating each month. Based on a cost per gallon of $2.86, it would cost approximately $57 per month to heat the home with propane.

A 100 pound propane cylinder holds approximately 23.6 gallons when completely full, and an 80,000 BTU appliance that ran 24 hours a day the propane would last about 1.12 days. If the appliance ran for 12 hours a day, the propane in the tank would last about 2.24 days.

1. How long should a propane tank last? Propane tanks are built for the long haul: on average, a high quality, properly maintained galvanized aboveground propane tank or propane cylinder should last 30 years or more, while some aluminum and composite cylinders can last even longer.

Gallon Propane Tank Costs A 120- to 325-gallon tank will take care of powering heating, cooking, fireplace, dryer, and standard hot water. However, you might want to spread out the number of times you refill it, in which case a 500-gallon tank would be more practical, only needing a refill every six months.

Rufus Youngblood, Director of Safety for Ferrellgas and a member of the technical committee for the NFPA 59 (Utility LP-Gas Plant Code), says if the propane container and valve are in good shape, storing propane for 10-30 years or more shouldn’t be a problem.

Unlike fuel sources that can degrade over time (kerosene, diesel, gasoline), propane fuel has no expiration date, nor will its potency suffer while being stored. The only thing you need to worry about when storing propane is maintaining the health and integrity of the propane storage tank.

A 20 lb propane tank will cost approximately $14-$20 to fill. The rate you pay depends on the refill cost, usually $3- $4 per gallon. Since a 20 lb tank holds about 4.7 gallons of propane, multiply the cost of propane per gallon by 4.7. For example, $3 X 4.7 = $14.10.

There are a couple other signs that your tank could be overfilled:

1. Your relief valve is released, and the sound of propane shoots out of the tank.
2. If your gauge is high after the tank is filled.