Closing off an atmospheric vent opening into chimney and flue
We are replacing our traditional natural gas fired, water heater with a tankless one. The old one was atmospherically vented into the chimney. The new one will be direct vented through the side of the house.
How should I close off the 4″ diameter opening into the chimney, into which my old eater’s galvanized vent was installed? What materials should I use besides cement/mortar? Will the opening in the clay liner need something specific to close off and seal the hole, so exhaust gasses from my furnace/boiler, which is vented into this chimney, do no leak into the chimney walls, etc.?
What are likely building codes regarding this?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part