I have a 50 gal Rheem Fury water heater (4" vent) and a Weil Mclain Direct Vent boiler (3" vent) in my mechanical room in the center of the finished basement. The vents off each appliance join an 8" existing (and soon the be removed) 8" double wall pipe that runs 18' vertically through the first floor and into and out of the attic. I am remodeling the first floor and the 8" pipe is right in the middle of my hallway.
I want to re-route those vent pipes. I have the first floor opened up and have 2 floor joist cavities that run perfectly to a exterior wall (10' horizontal run).
I know I can poke the Weil Mclain out the sidewall and be fine.
The Rheem water heater is a different story.
Running parallel and within 4" to the open floor joists is a new framed interior wall. I was originally thinking of splitting BOTH pipes off the union in the basement and sending them seperately about 2-1/2" on the 45 to that joist cavity - at the new wall - ; running them straight up against the wall (to frame a chase around them); and then having them 45 again in the attic and meet the union there rather than in the basement so I wouldn't have to make new holes in the roof.
#1) I don't know if 3" and 4" vents can run 18' vertically each with two to three 45s placed inline;
#2) I don't want to risk condensation in my boiler;
#3) if I sidewall the direct vent 3" vent, can the 4" make the run with 2 or 3 45s vertically and rejoin the 8" pipe exiting the roof by itself?