Understanding The 80% Fill Rule For Propane Tanks

image of a propane tank gauge and propane tank levels

It’s reasonable for customers to want to maximize each propane delivery. After all, a full tank enables uninterrupted heating for a long time. However, a quick peek at the gauge shows that propane tank levels are never filled to full capacity. They usually hover around 80% at most. So what’s going on? Well, it’s a precaution. There are no errors here. Propane delivery companies are merely complying with the 80% fill rule which is an industry-standard.

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Understanding Your Propane Tank Levels

In this article, we discuss the reasons behind the 80% propane tank rule.

Leaving Room For Propane Expansion

image of a residential propane tank

Heat makes most things expand. However, the rate of thermal expansion differs from one substance to another. For example, propane expands 17 times as much as water over the same increase in temperature. That might not be much of a problem in an open space but it is a major issue in an enclosed space. Propane tank dimensions are fixed and the walls won’t move. The best thing to do is to plan for expansion. Leave some room for propane to swell if it needs to in order to reduce tank stress. That’s why 20% of the capacity remains unused.

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The Effects Of Propane Tank Location

The tank’s location affects its temperature. For example, an underground installation enjoys greater insulation from the heat of the sun. Interior temperatures are likely to remain stable so the amount of fuel may be stretched a bit more than the usual 80% limit. Owners should not worry about the reduced buffer because the environmental conditions are favorable for the tank. If the tank is aboveground, then it should be sheltered from direct sunlight and heat sources. The fuel delivery company may also be consulted about additional insulation, if necessary.

It’s All About Propane Safety

image of paper cut out of family in hands depicting propane safety

If there were no free space inside, then any amount of expansion will immediately result in immense pressure against the tank walls. The structure might hold for minor increases in temperature but it could get dangerous with large temperature swings. Weak points can bust open and leaks may ensue. It’s best to err on the side of caution. All propane delivery services are mindful of propane’s tendency to drastically increase in volume. They will add more fuel into your tank until it reaches the 80% limit and stop there. The 20% buffer should be enough to keep you safe.

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The Effects Of Propane Tank Color

Propane tanks tend to be painted white or some other lighter shades. This is not just a matter of aesthetics. There is a scientific reason behind choosing a lighter hue. Physics teaches us that white surfaces tend to reflect light which allows them to stay cool. In contrast, black surfaces absorb light which results in fast heat build-up. This principle is best demonstrated by residential roofing. A light-colored roof can keep homes cooler than dark ones. When it comes to a propane tank, the content’s sensitivity to heat makes it crucial for the container to be of a lighter shade. Whatever you do, do not repaint this with a dark shade.

The Normalcy Of Propane Gauge Fluctuations

If you check your tank gauge throughout the day, then you might notice the readings fluctuate even when you don’t use any propane. This happens in a cycle day after day. Don’t worry because your gauge is probably fine. The amount of fuel has not changed. Small fluctuations are normal and may be attributed to temperature changes. You are likely to get a higher reading around noontime compared to midnight. Since it’s hotter midday, the propane expands and the gauge captures that movement. It shrinks back when the sun sets and cold reigns.

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The Insignificance Of Propane Tank Size

According to the rule, a 200-gallon tank can only hold up to 160 gallons of propane. The remaining 40 gallons of empty space will act as a buffer for expansion. A 500-gallon tank has a limit of 400 gallons of propane with 100 gallons for expansion. Some might think that a larger tank can get away with a smaller buffer percentage. If the 500-gallon tank were filled up to 90%, then it will have a 10% buffer of 50 gallons which is still substantial. However, the reality is that more contents will mean greater expansion when heated. The gap cannot be compromised. The 80% fill rule stands no matter the tank size.



Propane delivery is a well-thought-out process. The trucks come out with enough fuel for all customers and each household receives the amount they need. Service providers will check the tank size, determine the threshold, and fill up the container to a safe level. They will adhere to the 80% fill rule as a precaution against propane expansion. Homeowners will not have to worry about heat-related dangers. If you have more questions about the process, then don’t hesitate to ask your propane provider.

Call Wilcox Energy For Reliable Propane Delivery Services


When you need a reliable propane delivery service in the southern shoreline of Connecticut, be sure to contact Wilcox Energy. We offer high-quality fuel deliveries that are fast, affordable, and friendly.

You can count on Wilcox Energy to provide you with unbeatable service each and every time.

Give us a call today to discuss our different delivery plans and financing options.

We also offer a full line of HVAC services to enhance your home’s comfort and energy efficiency. Some of the services that we offer include heater tune-ups, furnace repairs, HVAC installations, and much, much more. Call now!

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Some of the areas we service include Centerbrook, Clinton, Essex, Westbrook, and these zip codes: 06409, 06413, 06426, 06498 as well as all surrounding areas in Middlesex County, Connecticut.

For more information about our propane deliveries or HVAC services, contact Wilcox Energy. You can click here to contact us or you can call us at (860) 399-6218. We offer a full line of affordable and trusted home comfort services.

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