How To Tell If A Propane Tank Is Empty

An image of empty propane tanks.

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Propane is one of the most popular heating fuels in most parts of the world. From cooking, grilling, and lighting, propane is an excellent choice for many households. However, using propane has one downside; most propane cylinder tanks do not have a fuel gauge. 

Often people run out of propane in the middle of cooking. Whether they’re using propane to fuel barbeque or in your usual cooking process, it’s quite frustrating. Of course, you do not want to be caught off-guard next time. So let us fix that. 
In this guide, we will delve into how to tell if your gas tank is empty. You will also learn which propane level is safe enough, how long an average propane tank lasts, and much more.

How Do I Know if My Propane Tank Is Empty?

Using any of the three methods below can help you to tell the amount of propane in your tank.

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Check the Propane Tank With Water

This is one of the simplest methods to tell if your propane is empty. The cool thing about it is that it is fast, convenient, and only requires a few items available around your home or campsite.

Here is how to test it.

Put some hot or warm water in a jug, a mug, or a small bucket. Whether it’s a 500 lb or 100 lb container is not very important. Just make sure the water is not boiling to avoid scalding yourself.

Next, disconnect the tank and pour the water down its side. Do not trickle, but pour the water so that it spreads out over a wide area. Trickling may cover only a narrow section of the tank, which might show unclear results.

Now, place your hand down the propane tank surface. How does it feel? The palm should feel warm from the top downwards to a certain level. Then the rest of the section downwards, your hand should feel cold. At the point of transition from the warm part to the cold section, that is the amount of propane in the tank.

If you feel warm along the entire surface, you know what that means; your gas tank is most likely about to run out or has reached unsafely low levels.

So what is going on? What happens is the liquified gas absorbs the warmth of the water, cooling it. That is why the part of the cylinder without gas retains the warmth.

Check By Weight

This should be a favorite method of how to tell if your propane tank is empty for people who love crunching numbers. It is basic arithmetics, though. You do not need to fret about it. 

For starters, you will require a scale for this method. What you need next is to figure out the weight of the empty tank, also known as the tare weight. That is labeled as “TW” on the tank collar.

Once you know the tare weight of your tank, it is now easy to tell the amount of gas left.

Let us find out how to do it.

1. Place the cylinder on a scale and note down its weight.

2. Next, subtract the weight of the empty cylinder(TW) from the total weight of cylinder+gas, you recorded above.

3. The figure you get is the weight of the gas left in the container. 

Let us demonstrate with an example of a 20 lbs propane tank. A 20 lbs propane tank weighs 17 lbs when empty and approximately 37 lbs when filled. If your cylinder tank weighs 27 lbs subtracting 17 lbs (TW), you get 10 lbs.

10 lbs is the remaining propane in your tank. To convert that into gallons, you simply divide by 4.2 lbs, which is the average weight of one gallon of propane. That shows the amount remaining in the tank is 2.4 gallons(10 lbs/4.2 lbs).

Use an External Pressure Gauge

If you want to avoid the hassles of lifting and weighing the tank or using the warm water method, then install an external pressure gauge as one of the parts of your propane tank. With the gauge, you only need to monitor its readings. Plus, it is more accurate as you get straight figures without doing conversions or other calculations.

Note that there are three types of pressure gauges:

Inline Pressure Gauge

This gauge is installed on the gas line between the tank cut-off valve and your cooking or grilling appliance. The inline pressure gauge lets you know the amount of propane in the tank, whether full or low.

Analog Propane Scales

Analog propane scales resemble analog luggage scales. The only difference is the figures indicated in the analog scales are net of the weight of the cylinder.

Digital Propane Scales

The digital gas tank placed on a scale analyzes the gas weight and provides a variety of data via an app on a smartphone. It is also an excellent way how to tell if your propane tank is empty. It allows you to determine the amount of gas remaining, cook time, gas fill percentages, and other metrics.

External pressure gauges are available in your local hardware store or online store. They come with an easy installation procedure.

How Low Can I Safely Let My Propane Gas Get?

Experts recommend monitoring the gas level keenly to avoid completely draining your propane gas tank. So what is the ideal gas low gas level?

The rule of thumb is to make sure the gas level doesn’t go below 20% of the tank capacity. Propane is affected by temperature levels and may condense at low temperatures. At below 20% tank capacity, the tank pressure is insufficient to sustain the appliances. 

The following are a few other potential problems.

Rusting of the Tank

Propane gas offers some form of insulation against rusting. An empty tank creates an environment for moisture and air, a perfect recipe for expiring and rusting. This condition degrades the structural integrity of the tank.

Gas Leakage.

Closely related to this is the potential gas leakage from the empty tank. Once gas runs out, most people forget to close the gas valves. The reasoning is that the tank is empty, so they do not consider it a huge problem. 

However, the empty has residue gas that evaporates into the surroundings and is a potential fire hazard. Here’s how to recognize potential leakage by smell.

Risk to Appliances and Property

Propane gas is an essential part of heating in most households. With the heating system not functioning, you risk losing the benefits of your essential appliances. This includes your cooking stove and propane showers. Not to mention freezing pipes during winter. These are some of the issues that can incur unnecessary and costly repairs.

How Long Does It Take for a Propane Tank to Run Out?

Knowing how long it takes for a gas tank to run out is essential for planning and budgeting. And this depends on several other factors:

  • The type of appliance, how many you have, and their BTU(British Thermal Unit) output per hour. For example, furnaces have higher BTU per hour than a grill.
  • The house size. A bigger house requires more heating and most likely has more occupants than smaller ones.
  • Individuals use patterns and intensity.
  • Seasons. You can expect more propane usage in heating during the winter.

Generally, a 20 lbs propane tank is expected to run for approximately 18-20 hours if used in basic cooking and light grilling. Larger appliances such as furnaces, heavy grilling, and water heaters require more gas.

You can also determine how long any tank size will last if you know the burn rate of your tank. And the burn rate is determined by the BTU output per hour of the appliance. As noted above, larger devices such as furnaces and large grills have a larger BTU output.

With this in mind, you can calculate the duration any propane tank size can last.

First, note that 1 gallon of propane output is approximately 91,500 BTUs. The next thing to figure out is the BTU capacity of the device per hour.

For example, a furnace with 100,000 BTUs output per hour can use 1 gallon of propane in 0.91 hours. You get this by dividing the BTU capacity of one gallon of propane by the furnace BTUs output per hour.

To figure out how long the propane will last, find out the capacity of the tank in gallons. You get this by dividing the propane amount by 4.2 lbs since 1 gallon of propane is equal to 4.2 lbs

Finally, divide the 80% of your tank capacity by the hourly burn rate of the appliance. That gives you the number of hours your tank will last using that particular appliance.

Final Thoughts

It is unfortunate to run out of propane when you need it most. Often that happens in the middle of cooking or grilling. The inconveniences, the frustrations, and the possible costs are numerous. That is why we recommend you always keep on monitoring the gas level. And as we demonstrated above, you have several excellent options on how to tell if your propane tank is empty. Use any of it to keep your propane gas appliances fueled and working.

Ryan McCabe

Ryan McCabe

Ryan is a home and small business energy expert, having overseen retail propane, heating oil, and HVAC services companies. On ComparePropane, Ryan writes about things that people should know when shopping for or using propane in their homes and businesses. 

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