The 80/20 Propane Tank Rule

Wondering why your propane tank doesn’t read 100% after a refill? There’s a reason for it and it is keeping you and your family safe. Propane’s properties are unique compared to other fuels and require protective and preventative measures. Read on to understand why Heller’s Gas leaves room for expansion.

Propane Expansion

Like many substances, propane expands when heated. Naturally, as a result of weather and environmental temperatures, propane expands 17 times the volume of water. The location of your tank may affect this expansion.

Underground Tanks 

You may be thinking, I have a propane tank and it is reading a bit above 80%. If this tank is below ground, there is no need to worry. An underground tank is partially insulated from the heat of an above ground environment. 

Tank Sizing

Regardless of the size of your tank, it’s safer to fill it to a maximum of 80% capacity. To determine what 80% in gallons would be for your tank, simply multiply 0.8 by the number of gallons your tank holds total. 

For example: 0.8 x a 250 gal tank = 200 gal propane capacity

Overfilling a Propane Tank

An overfilled propane tank will not have room for gas expansion. Overfilling could lead to problems such as leaks or even tank explosions. Excess propane could flow into the regulator causing it to freeze and disrupt the proper flow of gas to your appliances.


Heller’s Gas abides by the 80/20 rule to assure our customers are kept safe. Call our Care Center today to schedule service or delivery: 800-422-0560


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