Does My Bathroom Need a Return Vent
A home's heating, ventilation, and air conditioning (HVAC) system uses return air vents to facilitate air flow to and from the system's air ducts. Most rooms in the house that have an HVAC vent should also have a return vent, with the exception of the bathroom and kitchen.
Goal
Return vents increase the cooling and heating efficiency of the HVAC system. Without return vents in place, the HVAC system only pushes hot or cold air into individual rooms in a house, while air that has not been heated or cooled has nowhere to go unless a door or window is opened, which lets outside air into the house. A return vent extracts air from the room, making the effort of pushing heated or cooled air into the room easier for the HVAC system. In addition, return vents provide more air to the HVAC system to heat or cool it.
Each room against certain rooms
Because return vents help increase the efficiency of the HVAC system, installing a return vent in each room is more advantageous than installing return vents in just a few rooms. If the return vents can be closed, you can close the return vents in rooms that are warm or cool enough, which can attract more heated or cooled air to other rooms in the house.
Bathroom
Even if installing a return vent in each room increases the efficiency of the HVAC system, installing a return vent in a bathroom can cause problems. The main problem is that the air in a bathroom can be humid after someone takes a shower or bath, which is why the ceiling of a bathroom should have an exhaust fan to remove moist air. A bathroom return vent would draw in humid air, introducing moisture into the HVAC system, resulting in damage and reduced efficiency of the HVAC. In addition, unpleasant odors in the bathroom could be drawn into the HVAC system and distributed throughout the house.
Cooked
Installing a return vent in a kitchen is also a bad idea because a kitchen can also contain odors that you wouldn't want to spread in other rooms. Depending on the location of the return vent of a kitchen, it can draw moist air from a boiling pot on the stove, a dishwasher evacuating its hot and humid air or steam from hot water in the sink. In addition, cooking can produce small amounts of smoke, which can be drawn into the HVAC system through a kitchen return vent and possibly trigger smoke detectors in other parts of the house.