Hi all, sister selling house and inspection showed she needs a chimney liner for her furnace. It was swapped out a few years ago, and is apparently a high efficiency model, and the liner was not installed. I will be doing the install, and am curious of a few things. Is there a particular brand or material that is recommended? Do I attach lengths of pipe for vertical rise with screws, or foil tape, both? What diameter pipe, 3" or 4"? Thanks in advance. ducttapeman I thought i had it figured out, but after checking at local home supply store, am a bit confused. All they stock is the 'B', double walled, 3" or 4" ducting, that i assumed was for venting gas appliances w/out a chimney. Do you need to use this 'B' ducting inside of a chimney also? I intend to connect the water heater and the furnace together with a Y, before going through the basement wall into the chimney. Is it alright to use standard galvanized ducting before entering the chimney? They don't seem to have 'B' rated Y's that have a 3"(WH) and 4"(Furnace) inlet, and a 4" outlet.