Tankless water heater installation question

[JimNY]

Hello all!

I am in the process of installing a Rinnai tankless water heater. I checked online that the gas pipe needs a tail to be installed. Please see the photo with red arrow marked. However, I don't know what is the propose of that tail. Do I have to have it installed? Thank you for your helps!

 

[voletl]

That is a sediment trap
It is there incase any debris are in the pipe they will gall in the trap instead of into the unit possibly causing damage.

It needs to be installed
3 inches or more

 

[JimNY]

Thank you so much!