I'm not sure whether you are adding an exhaust vent fan to your bath or an additional HVAC vent/register to move more air. IF you are adding an exhaust vent fan or upgrading your existing exhaust vent fan may I highly suggest looking into replacing your switch for the exhaust fan or combo light/fan with a timed switch. I have learned that leaving our bath when I "thought" I was finished only left moisture in the air which actually leaves the bath area hotter than I would like it. I put a timed switch on our fan(s) in both baths and now we just turn the switch to the OFF position and the timer turns the fan OFF after twenty minutes. The bath(s) are always cooler now.