Why Didn’t We Fill Your Propane Tank to 100 Percent?

Written By: on September 18, 2023

Let’s talk about the 80 percent fill rule.

propane delivery flagstaff, az When was the last time you looked at your propane tank’s gauge? Countless Superior Propane customers in Flagstaff, Williams, Sedona, Prescott and other northern Arizona towns use our automatic propane delivery option and don’t look at their gauges for months.

Some are surprised to find that, after their propane delivery, their tank is not 100 percent full. You don’t need to worry. We aren’t shortchanging you on fuel. Your tank gauge might be lower (or higher) than you’d expect for several reasons.

Propane volume expansion

Propane, like water, expands and contracts as outdoor temperatures rise and fall. However, propane’s volume (the amount of space it takes up) will grow 17 times more than water’s with the same temperature increase.

Considering how significantly propane’s volume shifts, you can see that the amount of space it occupies is contingent on weather conditions.

Why your tank’s fill percentage might change

The gauge on your home’s propane tank does not measure the number of gallons in your tank. It measures the percentage of the tank that contains fuel. There’s a float that rests on top of your propane. The higher this float rests, the higher the percentage reading on your gauge.

But as we’ve already established, the temperature outside affects propane’s volume. So, if we fill your 250-gallon propane tank with 200 gallons of fuel in moderate weather (say, 60°F), the gauge would read 80 percent. But if there is a sudden temperature drop in the evening, the tank’s fill percentage will drop slightly as the fuel’s volume contracts. There would still be 200 gallons of propane in your tank, but they take up less space.

The 80 percent propane fill rule

This brings us to why we (and all other propane companies) never fill an aboveground propane tank more than 80 percent. Leaving 20 percent of your propane tank empty creates a space allowance for the fuel expansion that can happen during periods of extreme heat. Responsible fuel companies follow this standard safety process to ensure your tank doesn’t experience dangerously high pressure.

And remember, we only charge you for the propane we put into your tank. You don’t need to worry about paying for a higher fill than you’re receiving.

Watch out for 20 percent!

If you’re still contacting us whenever you need a propane delivery, it’s important not to let your fuel levels drop to 20 percent. Doing so, especially in colder weather, increases the likelihood of an unexpected runout. We recommend calling us for a delivery when your gauge hits 30 percent instead.

Even better, you can sign up for our FREE “Keep Full” automatic delivery service. With this option, Superior Propane’s state-of-the-art system will track your fuel usage, and we’ll refill your tank before you run low. Plus, we’ll give you a discount on your propane just for enrolling!

If you want to enroll in automatic delivery, contact the Superior Propane office today.