Hi,
Finishing off the basement. I am wondering how to know where a cool air return is needed and what it's purpose is. Where does it fit into the rest of the heating/cooling forced air ductwork?
Thanks,
Kim E.

 

Forced air systems are basically closed systems. What that means is the cold air return takes air from the rooms into the system, conditions the air and then distributes that conditioned air into the rooms. They are referred to as cold air returns because they are usually found at the floor level where the coolest air in the room is. If they were located at the ceiling they would be taking in the warmest air in the room.

On your furnace you'll see ducts that come off the top of the unit and at the bottom. Usually the duct at the bottom is the return duct and at the top is the supply duct. The return duct usually have the air filter in or near it. Its primary purpose to to keep your unit clean.

The volume of the air in a room remains constant. What that means is you cannot blow air into a room without taking out the same volume of air from the room. Let's say you finish off your basement without a return. But there are returns located on the levels above the basement. The supply vents in the basement blow out cool or warm air depending on the season. Since the same volume of air must leave the basement that is being blown in by your supply vents and the returns are located upstairs, which type of air will rise to go upstairs to the returns, the warm air or cool air? Naturally the warm air will rise and the cool air will sit at the floor of the basement. This will make the basement cold in the winter and too cool in the summer. By installing a cold air return at floor level in the basement makes the basement a lot more comfortable in the winter. By closing this return and adjusting the supply vents in the summer, prevents the basement from over cooling.