My home was built in the 1960s in MD, USA and has a ground floor bathroom next to the garage. The bathroom has a heating vent in the wall bordering the garage. (The wall is 2x4, not 2x6, construction, so it has minimal insulation.) Someone told me that it is against current code to have a heating vent in an exterior wall and that the garage is considered exterior space. Is this correct? If the bathroom were to be updated would I have to move the vent? Would it be grandfathered?