I own a home in MI that was built in 2005. It has two high efficiency furnaces (zoned for each floor), and what I am calling a high efficiency hot water heater (heater is electronically cycled and PVC exhaust duct with blower assist to the outside).
My question: I recently built a deck behind the house, and for several reasons was forced to place the floor of the deck about 2 inches below the hot water tank exhaust duct. The issue I have with this is that the exhaust duct has a 45 elbow installed so the air is blowing directly on the deck surface (which also increased the noise of the exhaust when it cycles). My PVC furnace vents exit on the side of the house about 30 feet away. Since both the furnaces are high efficiency with low temperature exhaust and a blower to force the exhaust out of the house, and so is the hot water tank....(here is my question)...can I buy a y-pipe of 3.5" PVC and couple my hot water tank exhaust to one of my furnace exhausts? the pressure/CFM appears to be low enough where backpressure should not be an issue. What should I consider if, in fact, I can couple the systems? The benefit for me (if I can do this) would be that I could use the old hole through the house for the hot water tank to route my NG line for my grill on the deck!!! (I would really like to avoid making another hole through the wall).