Understanding the 80/20 Rule for Propane Tank Fill-Ups

What Homeowners Need to Know

After we make a delivery to your tank, you might notice that it's never completely full, but instead filled to about 80%. This is actually a safety measure. Propane exists as both a liquid and a gas inside the tank, and the 80% rule ensures there’s enough room for the liquid propane to expand safely as temperatures change.

The remaining 20% of the tank is called "vapor space." It’s necessary for the tank to work properly, preventing over-pressurization and keeping your propane system running smoothly year-round.

Why Only 80%?

Propane expands and contracts with temperature changes. When the temperature rises, propane in its liquid form can expand. The 80% fill ensures there’s enough space for the liquid to expand without causing excess pressure inside the tank. If the tank were filled to 100%, there wouldn’t be enough room for the propane to safely expand, which could cause issues with pressure.

That 20% vapor space is critical for the proper functioning of the tank. It helps stabilize the tank and makes sure everything works as it should, even as temperatures fluctuate outside.

Propane Safety is Key

The 80/20 rule isn’t just a guideline—it’s there to keep your home and family safe. By understanding the need for this space, you can be confident that your propane tank is being filled properly and safely.

If you have any questions about propane or want to schedule a delivery, don’t hesitate to reach out. We’re here to help!