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Propane Tanks: The 80/20 Rule

Why is My Propane Tank Filled Only to 80 Percent?


If you’ve ever checked your propane tank right after a propane delivery, seen the gauge level at 80 percent and scratched your head in confusion, read on.
Your ProGas delivery technician didn’t short you when they filled your propane tank – they are simply following an important safety rule based on the science of propane gas.

The Science of Propane

Liquid propane is like water in that it expands in the heat. But it expands a whole lot more than water – about 17 times the volume of water over the same temperature increase.

When that expansion happens, the propane needs somewhere to go. That’s what the 20 percent empty space in your propane tank is there for. It provides the room your propane needs to safely expand.

This rule of filling a propane gas tank is called the 80/20 rule of propane safety. If your propane tank is 500 gallons, it can only be safely filled to 400 gallons. An underground propane tank may be filled slightly more than 80 percent because the ground insulates it from heat and temperature fluctuations.

Please note: changes in temperature may also cause some fluctuations in your propane tank’s gauge reading. This is perfectly normal! The amount of propane in your tank hasn’t changed, the propane has simply expanded. When the temperature goes down, so will the gauge level.

Speaking of safety, there’s a reason your propane tank is painted a light color. Lighter colors reflect outside heat; darker colors absorb the heat, which can cause the propane in the tank to expand to dangerous levels. Never paint your propane tank any kind of dark color!

Count on Progas For Reliable Propane Delivery

Keeping your propane tank filled is even easier with our Keep Full automatic delivery program. Our professionals track your home’s or business’s propane usage and schedule delivery before your tank runs low. ProGas also offers wireless propane tank monitors for precise monitoring of your propane usage 24/7. No need to check your propane tank gauge or call to schedule a delivery.

For safe, dependable propane delivery throughout our service area in greater Pittsburgh, Ohio and West Virginia, no one beats ProGas. Contact us today and become a ProGas customer!