Orphaned Water Heater Flue Requirements

[Shane Pouch]

Hello to all,

I have a question regarding the re-lining of a 6" Type-B furnace flue stack that now only serves an orphaned water heater.

I am getting conflicting information about whether the 3" liner has to be Type-B pipe or not.

Which is it, and why?

Thanks.

[Jon Randolph]

Don't quote me on this, other will likely be along shortly.

I the vent goes un-protected through an unconditioned space, such as an attic, it needs to be class b. If it will go entirely through an old chimney chase, single wall.

[Bob Harper]

The flue can be up to 7x the size of the smallest appliance. However, it will perform like a dog. It should be re-vented using B-vent installed to the listed instructions. If it vents into a chimney, it should be relined sized to the WH. It isn't up to the H.I. to specify the liner size, only it needs to be sized to fit that appliance and let the pros size it, whether B-vent or liner.

Single walled vent connector not allowed in unconditioned spaces or as chimney liner. Listed liner only.

HTH,
Bob