Guys this is what you get when you hire a low bid contractor. This was on a 2 story house with gas fired furnace located interior first floor closet on the back side of a 1/2 bath. When I am inspecting a two story with gas furnace I have two thoughts on my mind where does the flue pipe exit the home and where and how is the return air installed.
This set up was crazy the supply air ducts to the second story were not visible they were in the floor of the second story. The return air was using 3 floor joist chases between the first and second levels with return air grills located in the hall floor upstairs. These grills had openings that were large enough for me to get my head in. Here is what I found staring back at me.
The furnace flue pipe just barely visible in the pic was in the return. The small duct that is open on both ends was suppose to be for the downstairs bathroom exhaust fan. With the duct open the return air was being drawn from both open duct ends one being the fan and the other from the attic above the garage and when the fan was in operation it was discharging the aroma from the commode into the return.
As I am typing this post I am wondering how many inspectors would have missed this as it is not something that just glares out at you. One has to be aware of where the furnace is installed. This furnace should have never been installed where it was should have been out in the garage but would have required more duct to be installed. This is what you have a mess to try and make safe.