HVAC stands for heating, ventilating, and air conditioning. The HVAC systems are used in industries, commercial and residential buildings where humidity and temperature need to be closely regulated. The filtration systems in general can be classified as Liquid -Solid separation (e.g. vacuum and pressure filters), Air-Gas separation (e.g. activated carbon filters) and Air-Solid separation (i.e. filters that remove particulate matter from air). HVAC filters belong to the category of air filtration products. Filter media used in air filters are nonwoven fabrics laid perpendicular to the air flow to arrest the solid particulate matter. Air filters can be either mechanical filters or electrostatic filters (electrostatically enhanced filters). Most of the filters fall under the category of mechanical filters and depend on four primary filtration mechanisms - sieving, impaction, interception, and diffusion. Filters are characterized by their filtration efficiency, MERV rating and Micron size. HVAC filters are used in split and window type air conditioners as well as centralized air conditioning. The requirement of filter media for split/window type air conditioners varies from manufacturer to manufacturer and this media is generally washable.