Equipment
Rebates
Have you ever looked at your propane tank gauge right after a delivery and wondered why it doesn’t read 100% full? It might seem like you didn’t quite get what you paid for—but don’t worry. There’s a very important safety reason behind this, and it’s called the 80/20 rule (sometimes just the “80% rule”).
This practice isn’t a trick or mistake. It’s a safeguard that keeps your home, your family, and your property safe. Let’s take a closer look at why propane tanks are never filled to the brim and what it means for you as a propane user.
Propane is stored inside your tank as a liquid, which later turns into gas before it powers your appliances. That’s why propane is sometimes called liquid petroleum gas (LPG).
Here’s the key difference: propane is highly sensitive to temperature changes and expands much more than water. In fact, propane expands 17 times more than water when exposed to the same rise in temperature.
That expansion has to happen somewhere. If a propane tank were filled completely to 100%, there would be no room left for the liquid propane to expand safely. Instead, pressure would build up inside the tank, creating a dangerous situation.
That’s why propane delivery drivers fill aboveground tanks only to about 80% capacity, leaving 20% as space to allow for safe expansion. Underground tanks, which are naturally insulated from extreme heat, can sometimes be filled a bit higher, but they also follow the same principle.
For example:
This rule is especially important during the summer, when high daytime temperatures can cause propane to expand rapidly. If you notice your gauge reading moving up or down a little during big temperature swings—say, a hot afternoon followed by a cool night—that’s perfectly normal. The actual amount of propane hasn’t changed; only its density has.
One more tip: never paint your outdoor propane tank a dark color. Dark colors absorb heat, which increases propane expansion inside the tank. Sticking with lighter colors helps keep your storage system safe and stable.
If you’re not sure where your tank gauge is, check under the dome on top of your tank. It looks like a meat thermometer.
The gauge doesn’t measure gallons of propane—it measures the percentage of the tank’s capacity. For example, if your gauge reads 50% on a 500-gallon tank, that means you have about 250 gallons left.
Here’s the key number to remember:
That gives your propane company enough time to add you to their delivery route before you risk running too low.
Between work, family, and everything else, it’s easy to forget about checking your propane gauge. But forgetting could leave you in a tough spot. Running out of propane isn’t just inconvenient—it can be costly.
If you run out completely, you’ll need:
That’s why many propane companies in Tennessee offer automatic delivery. This service uses your past usage history and current weather conditions to estimate your fuel needs. The company then schedules deliveries before you run low—so you don’t have to lift a finger.
Some suppliers even provide wireless tank monitoring. These small devices attach to your tank and send real-time data about your fuel levels. Both you and your propane provider can track your supply through a smartphone app, which takes the guesswork out of the process.
Of course, if you prefer more control, you can always stick with calling in your delivery. Just remember that when you’re managing orders yourself, it’s best to give your supplier a few days’ notice. While some companies can make next-day emergency deliveries, having a plan keeps costs lower and ensures you don’t run out during peak demand times.
Check with your local Tennessee propane company to find out which services they offer. With the right setup, you’ll always have the fuel you need, right when you need it.
