Flexible vent on gas water heater?

Is this flexible vent permissible? (natural draft gas fired water heater)
My understanding is that it should be single wall galvanized vent.

Thanks in advance!

It’s hard to say whether that is a listed vent piping (does not appear to be), but its installation is improper. It needs to be corrected.

Jeff… You mentioned that the installation is improper. Could you elaborate? I am concerned about whether the vent is a listed material, the connections and that the furnace connects into the B-Vent above the water heater.

It should be on a constant rise of a 1/4inch per foot minimum…

I’ve never seen “listed” flex duct.

It does exist in both single wall and double wall (B-vent) types. They will typically include factory installed collar connections and come in pre-manufactured lengths.

It has a negative pitch as it leaves the water heater. That is not allowed.



Good article, Juan.

Thanks Juan. I learn something every day here.

I have read a lot of his blogs he definitely has a gift.

certain areas of Tucson allow flex and some don’t, probably the same in your area