A drip leg is certainly not a well-known apparatus. You would not be the first to wonder what on earth it is, what its purpose is, and why it is necessary.
If you had to guess by the name, you aren’t likely to have much deductive success. Thankfully, I am taking the guesswork out of it and will provide you with the necessary definition and information to answer your questions and clear up any misunderstandings.
A drip leg is a trap installed on a wet gas (propane/butane) pipeline to catch condensate before it can enter the gas meter and create problems in the gas assembly. Drip legs are required at the meter outlet for any appliance using wet gases, where condensate can occur in the pipes.
Drip Leg Definition
According to Section G2403 of the International Residential Code (IRC), a drip leg (referred to as a “drip”) is defined as follows:
“The container placed at a low point in a system of piping to collect condensate and from which the condensate is removable.”
Let me clarify the “piping” mentioned in the IRC’s definition since that seems like a massive category without proper context. Chapter 24 in the IRC is about fuel gas, meaning that a drip leg is installed for fuel gas piping.
This drip leg is akin to a bathroom fan condensation trap, which you might be more familiar with; it catches condensing water and prevents liquid from gathering where it shouldn’t.
When Are Drip Legs Required?
Drip legs are required for appliances that use wet gas; they catch the resultant condensate. You might be more familiar with calling it liquified petroleum gas (LPG), propane, or butane.
Wet gas has a higher liquid content of hydrocarbon compounds (such as ethane, butane, and propane) compared to the methane content. As a result, these compounds can condense out of the gas as a liquid.
Dry gas has much more methane than the other compounds, which means that there is little that can condense out of the gas and a drip leg is not necessary.
What Is the Purpose of Drip Legs?
Drip legs (also called dirt legs or drip tees) keep condensate out of your gas appliance.
If the trap wasn’t present to remove the moisture, it could get into the gas assembly. This can interfere with the gas flow and combustion, which can cause safety issues and can impact the function and longevity of the machine.
When you have anything that impacts gas flow and combustion, there is the risk of ignition issues and overheating. This can lead to fires and gas leakages.
Let me quickly clarify: a drip leg and a sediment trap are different apparatuses.
A sediment trap performs a turn in the pipe to deposit sediment (and moisture), keeping dirt out of the gas appliance. Preventing it from clogging the burner and gas valve.
A sediment trap can catch moisture, while a drip leg cannot catch sediment.
This is because a drip leg does not change direction. It just has a trap that drops away from the main line (like a “T”), meaning that moisture (and some sediment) will be deposited, but smaller dirt particles can also be carried over the trap when suspended in the gas.
Even though both apparatuses are traps, the IRC lists drips (G2419.2) and sediment traps (G2419.4) under different sections. The similar appearances and some crossovers in function likely add to the confusion.
Domestic Systems Requiring Drip Legs
The household appliances and systems that require a drip leg are those that use wet gases. You may be more familiar with these natural gas liquids (NGLs) or liquified petroleum gases (LPGs) being referred to as butane, propane, isobutane, ethane, and pentane.
Now that wet gases sound much more relevant to household functioning, we can talk about where it is used. Typically, you will find liquid propane and butane supplied in homes in large storage tanks.
If the appliance uses a wet gas, it needs a drip leg.
Where Are the Drip Legs Located?
According to Section G2419.2, drip legs must be installed at the outlet for the gas meter. This placement allows the drip to act as a trap and prevents the gathering of condensation in the pipes, where it can block gas flow and run into the gas meter.
Section G2419.3 says that the drip legs must be readily accessible for cleaning and to empty out condensation. Additionally, drip legs are not allowed to be located where the moisture can freeze.
You need to be able to clean out the condensation from the trap, so it must be accessible since it is undesirable to have condensation in the gas line. This cleaning should be done whenever the appliance is serviced and repaired.
Drip legs are designed to collect moisture. If that moisture freezes and expands, then, like with plumbing pipes, your gas pipe can crack. It is dangerous to have a compromised gas line as this can leak gas into your home.
Propane and butane are mostly odorless and colorless gases that are highly flammable (risk of fire and explosions) and displace oxygen. This means that in low or high concentrations of the gas, you can see varying degrees of symptoms associated with suffocation.
Drip Legs in Commercial Applications
Drip legs also have a different use when it comes to commercial buildings. Drip legs are staggered throughout steam systems (like large boiler systems) to collect condensate.
However, considering these systems are part of apartment buildings, you wouldn’t be responsible for these drip legs. You aren’t even responsible for any other gas-related drip legs.