HVAC grilles and diffusers are the exit ventilation points for heating, ventilation and air conditioning (HVAC) systems. Although they are occasionally used as return vents, their primary purpose is to introduce conditioned air into the space so that it is evenly distributed and mixed with minimal noise. HVAC grilles and diffusers come in a variety of standard sizes, usually square, rectangular or round; they usually have a set of louvers or fins that direct airflow in a pre-set pattern. Larger industrial grilles and diffuser may include adjustable louvers or dampers that can be adjusted manually or automatically to control airflow. Although diffusers are often seen as decorative grilles for inlet vents, they play a vital role in the effectiveness of HVAC systems and should be properly matched to any given application.