I'm finishing my half story and I currently have one supply vent in the bedroom. That vent runs straight up from the cellar, which is about 12 feet below the register. I have a bathroom in the half story as well, and it currently has no supply vent. The only practical way to get one there is to run it off of the same duct in the bedroom. It would be routed through the side attic, probably about 20 feet in total, to get to the bathroom. Would this be beneficial for getting heat/air to the bathroom, or is that too much to get from one supply duct off the the trunk in the cellar? I don't know what the cfm's are from the existing vent, but it blows fairly strong.