Every home and building that uses forced hot air for heating purposes will have return vents. The return vent, or register, is also known as an air return vent, and a cold air return vent. It accomplishes just what the various names imply, return colder air, via registers and ductwork, to the furnace so that it will run as designed. Return vents also provide proper air circulation throughout the structure. A return vent, will, as well, be installed with central air conditioning systems, though in a somewhat different configuration.
Air return vents are necessary to prevent a buildup of pressure in the structure that may lead to various health problems, as well as preventing mold and mildew, and deterioration of the structure due to moisture buildup. As warm air is forced into a room, it replaces cold air already in the room. This cooler air must be pushed out of the room; otherwise the room becomes uncomfortably over-pressurized. The cooler air is, in turn, forced into the return vent, back to the furnace, reheated, and returned to the cycle.
The size, location, and length of heating, ventilating, and air conditioning (HVAC) registers and ductwork are determined by measurement of air movement at cubic feet per minute (CFM). Whatever the CFM output of the heating or cooling system, the air return vents must be able to provide the same CFM ratio. Additionally, for maximum heating and circulating efficiency, there should be properly-sized return vents in each room where heating registers are located.
Heating and air conditioning registers are located on the outside walls of structures, air return vents on the inside walls. This is because the warmed or cooled air at the outside perimeter of a room forces the cooler or warmer air already in the room toward the center of the structure. From there, cooler air is circulated via return vents to the furnace for more efficient operation. In the case of air conditioning, the warm air in the room is forced to the return register, and vented outside the structure.
Unfortunately, most homeowners are unaware of the importance that a well-designed, properly-functioning air return system has in assuring correct air circulation. Maintaining the return vent, or vents is very important, however, and often a matter of simply unscrewing and removing the grille, vacuuming inside the return register, and inspecting duct seams. Additionally, an unsightly grill can be repainted, or replaced just as easily. Assuming a properly designed installation, and timely maintenance/cleaning, a return vent system will be attractive and fully functional for many years.