possible problem...3" and 4" ducting
It is a large master bathroom, the only venting to outside is in the 'enclosed' toilet area (bath fan and window). This is the reason I need to vent the shower area.
I just found that the existing ducting (from the toilet room to outside) is 3". The intended bath fan I'd like to install in the shower requires 4" ducting. Does this mean that I am out of luck in trying to tie the 2 bath fans into the same outside vent? I assume the 4" ducting above the shower would lose efficiency if I tap into the existing 3" ducting.
If so, my choices appear to be:
1) Run a separate 4" duct for the shower and cut a new vent in my siding for it
2) Upgrade my toilet fan to a 4" duct, enlarge the existing vent, and tie the 2 together.
3) Let the 4" duct share the 3" duct/vent and hope efficiency is OK