This forum is great, the knowledge here is unbelievable!
At this time I have a 60k BTU furance that serves my basement.
We're replacing the old 80% for the 1st floor on a few weeks with a a new 90% high efficiency furnace.
Presently the 60k btu 90+ that is in the basement venting goes from 2" in the basement (from the furnace) and is upsized ahortly thereafter beacuse of the the length of the run (per the table) to a 3" and runs up inside the wall and up into the attic, the 3" pvc runs up in the attic and out through the roof. I t may be upsized again to 4" before but I can't remember, regardless the guy that originally did it knew what he was doing.
(Originally we had it tun out the wall but the exhaust all over the window was a nuicance so we had it changed)
Anyway , the new furnace will be in the basement - Can I run the PVC right from the furnace, it would make a perfect 90 out of the furnace and then run straight up inside the wall (or empty cavity) and then pop out in the attic,
Question is this - can it be tied into the the 3" ( or 4")of the 60k btu (that serves only the basement) T'd into the same PVC exhauust as the new 80k BTU 90% furnace (that will serve first floor) of our Ranch, the T would be in the attic and this way I could have one roof penetration?
Rather than poking another hole in the roof could I just upsize the exisitng 3" penetration to a 4", 5" or 6"?