Registers are the vents in a heating, vacuum and air conditioning system that allow air leaving the ducts to enter a room while grilles cover the return vents to the air handler. Registers often have a damper that allows the home occupant to adjust the air flow from the duct while grilles do not. In some homes, the installer places additional grilles in walls or doors to facilitate the return of air to the air handler from closed rooms.
Both registers and grilles are slatted grates. Installers may place them in floors, walls or ceilings, depending on the configuration of the HVAC system. The louvers on registers direct the air in one to four different directions to increase comfort in a room.
With some HVAC systems, the filter is behind the return air grill. These grills are usually hinged and have an easy-to-open latch for replacement. Replacing the filter on a regular basis improves the efficiency and protects the system.
Over time, the finish on both registers and grilles deteriorates, so owners sometimes replace them to improve the aesthetics of the room. The measurement of the duct itself and not that of the old unit determines the correct replacement size. Home improvement stores offer both types of grates in a variety of finishes and materials.