I had a question regarding the deference between a drip leg and a sediment trap on gas water heaters and furnaces. I was able to find an answer and thought I would post it here for the benefit of the community:
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Sediment Trap vs. Drip Leg
“Drip leg” and “sediment trap” are often used interchangeably, but they are really two different things. Drip legs (technically call just a “drip”) are installed to collect condensation in a gas piping system, so they are installed in a low point to prevent condensation from running back into the gas meter. Wondering why you have never seen one of these? They are not required where the local gas utility provides “dry gas” – which is defined as “a gas having a moisture and hydrocarbon dew point below any normal temperature to which the gas piping is exposed. On the other hand, sediments traps are installed to collect sediment, rust, or debris in a gas piping system that can clog a gas appliance burner and cause a malfunction."
Where to Install
This section of the plumbing code has been changing in the last few code cycles, creating some confusion. For a while, sediment traps were required “as close as practical” to the appliance, which lead many installers to put the sediment trap after the flexible gas connector. The 2016 CPC clarified that the trap should be installed after the appliance shutoff valve, but before the flex connector. Presumably, this is to facilitate cleaning the trap.
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“It is not uncommon for me to find a gas line sediment trap that has been installed wrong. When looking at the photos below, keep in mind that gas is usually very clean, and there is not that much, if any sediment in gas lines. The sediment in the photos is exaggerated for instructional purposes.”
“One last tidbit of information worth noting. Although not visible in the photos, the sediment traps are AFTER the shut off valve. If the sediment trap ever actually gets serviced, the technician can shut off the gas and open the trap. If the sediment traps were BEFORE the shut off valve, all of the gas in the house would need to be shut off in order to service the trap.”
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thank you.
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Very well explained. I will be removing the wording Drip Leg from my reports and just using Sediment Trap.
Thank you
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On this topic of moisture and sediment, I was told by two plumbers that the Corrugated flex pipe works as both, and the sediment and moisture will settle in the corrugated low spots. I don’t know if I can believe that. They each said the flow velocity of gas is so low that once settled it will stay in the flex cavities. I am suspicious if that is true. If it is true, I remain suspicious if when a person disturbs the flex line or the flex line gets whacked accidentally or intentionally, the sediment then flies towards the appliance burner. Is there any truth to these plumbers’ tales?
Thought they were the same. I have both terms interchangeable. Good explanation above.
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They are the same thing.
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Can you post the source if your information from a fuel gas code book?
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Way to throw a wrench into the works, LOL, now you did it. 
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Dirt leg, sediment trap or drip leg are all interchangeable. In modern code books there will be a reference to a sediment trap.
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Martin,
While many people may use these terms interchangeably, they are doing so mistakenly. I will prove it to you, and for anyone else reading this. I am going to first reference from the ICC (International Code Counsel) 2021 IFGC (International Fuel Gas Code). The ICC is the authority from which localities use to adopt their local codes from. If the locality decides to make changes (usually minimal changes here and there) that locality will created there own code that is mainly based off the ICC code. For the next example I will reference from the 2019 California Plumbing Code for a local code reference.
You will see that both of these codes clearly define these as different components with different purposes. You will see that the 2019 CPC could be the culprit for spreading this misinformation as the first paragraph mentions the two terms together, but the misunderstanding is also due to the reader not reading further into the code.
I think I’m going to go with the master plumber on this one…
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This experiment below is why everyone needs to trust but verify, even from a master plumber lol. Think for yourself, and verify for your self!
The Milgram experiment(s) on obedience to authority figures was a series of social psychology experiments conducted by Yale University psychologist Stanley Milgram. They measured the willingness of study participants, men from a diverse range of occupations with varying levels of education, to obey an authority figure who instructed them to perform acts conflicting with their personal. Participants were led to believe that they were assisting an unrelated experiment, in which they had to administer electric shocks to a “learner”. These fake electric shocks gradually increased to levels that would have been fatal had they been real.
So what is a wet gas and how is it measured to be wet? Don’t quote from Wikipedia and where is it present today? Why have natural gas systems operated properly for 50+ years without the use of a drip leg when a sediment trap has been used for almost the same amount of time? Is the moisture removed from the natural gas before it enters your home? If natural gas has moisture requiring a drip leg would it not begin to corrode the steel gas pipe?
Last question. Have you ever removed the cap off of a sediment trap and inspected its contents? What did you see?
I won’t use the graphics that you took from space city inspections.
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