Not sure if this helps at all, but my chimney has 2 shafts…one for what I assume is for the furnace and the second could be for that second exhaust pipe in the basement (maybe for the old gas hot water tank, it was swapped to electric in 2010, or maybe earlier)…however our house also has a decommissioned fireplace…so the second chimney shaft could be for the fireplace. I may have to talk to a professional.
…and I’m going to buy another carbon monoxide detector for the utility room.
Having a hard time figuring out where to expel my used stank air.
Thanks for chiming in everyone!!