2" furnace filters are available in many standard and non-standard sizes. Simply select your size from below to choose your filter size. Another most important you must know is that hvac filters, furnace filters and ac filters are almost always the same thing. The most important thing to know is the correct length, width and thickness for your replacement air filter. Keep in mind that length and width are reversible (i.e. a 15x20x2 is the same as a 20x15x2).