
Furnace exhaust into chimney flue?
I’m trying to identify what sort of mortar or sealant is used currently when replacing a furnace exhaust pipe into a flue. I know this isn’t code but I’m not a plumber or HVAC guy so IDK what’s currently being used instead of the set up at my house. I’m hesitant to use any sort of mortar or cement (assuming I have to bust it out). I’m hoping I can slide the pipe out and use 3m fire sealant. Any ideas? Thanks!