It is a sediment trap, and actually, you shouldn’t.

A long time ago, The natural gas that came to the house had a fair amount of sediment and moisture. At least I think it did, because plumbing codes required a method of removing said sediment before every gas appliance in the house. Want to see the code? Click: Here and read 408.4

The idea is simple; if the valve in a furnace closes on a bit of dust, the valve would stay open a little bit even after the furnace turns off. Raw gas would move around that dust and could ignite outside the furnace.

No good. So a sediment trap (or dirt tee) was invented. Gas from the gas company comes down a pipe, and the pipe takes a 90 degree turn into the appliance. Straight down from that is a section of pipe with a cap. Any moisture in the line misses the turn and drops into the lower pipe.

Thing is, our supply of gas in this country is incredibly clean. So the chances of a valve closing on a bit of dust is between zero and oh, never mind.

Still, for peace of mind, make sure that when a gas appliance is installed, a sediment trap is installed as well.

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About the author

Joe has many years of experience as a Home Inspector. Joe is a proud member of ASHI, MAHI, WAHI & SAAR. He follows the Best Practices as described by the American Association of Home Inspectors and the Wisconsin Association of Home Inspectors. He is licensed in Wisconsin and is Radon Certified. Joe also complies with ASHI's Code of Ethics.

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