The bathroom vent you see on the picture is slightly above the floor level (it’s actually just a register, fan motor installed in the attic above), and I personally guarantee that in this location works like a charm (there’s one more bathroom vent above the shower stall).
The reason for placing the bathroom vent motor in the attic and running an exhaust duct behind the toilet was that some jurisdictions do not allow to have the bathroom vent assembly installed lower than any sink, tub, toilet edge or shower head. Installing bathroom exhaust on GFCI protected circuit could be another solution but check with your local building department before installation.
Building code paragraphs concerning bathroom ventilation based on 2006 IRC (International Residential Code):
CFM – cubic feet per minute – general term used to specify the amount of air that the bathroom vent / fan (in our case) is able to move within one minute of its operation.
If you install the bathroom vent / fan directly above the tub or shower, it must be listed as suitable for such locations, and must be installed on a GFCI protected circuit – this is every manufacturer’s (not the code’s) requirement.
The exhaust fan sizing formula is very simple … actually there are three simple methods to do it (click the image or link below).
Calculations are based on the size of your bathroom and you can do it manually or use my Bathroom Vent Calculator – enjoy it.
Search existing Q&A in Bathroom Questions
This article was written by Dariusz Rudnicki
I'm a retired Illinois home inspector, founder and editor of checkthishouse.com, a blog which attracts around 2 thousand readers daily and is dedicated to answering the many questions of home owners and home buyers. Connect with me on Google+ Find me on Google+ Local