Bruce, I hope your comment about cutting the hole being a "reasonably good job" was sarcastic.

In addition to being too close to the ceiling, not being secured to the vent, hacking a hole into listing venting thereby voiding the listing of the venting and probably both appliances, inspect the rest of the venting,.........well, you get the idea.

FYI, it would be a "siamese" technically since two merge into one whereas a "wye" splits, but you have the right idea and yes, that is what most people refer to them as.

This just makes it more convenient for the flue gases to spill out higher up so they don't have to spill all the way down at the draft hood. Makes for a more efficient CO distribution system. I trust the furnace has plenty of return leaks to gobble up any flue gas spillage and distribute it throughout the home in the most efficient manner possible? You said "closet" so can we assume they didn't ruin this CO distribution system with a balanced, properly sized powered makeup air system did they? Rotten buggers....


-I hope you all catch my sarcasm in this post.
Bob

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disgusted with some people on this forum. Out of here!