Air filter uses basic hardware store furnace filters. Squeeze to release screen, Buy a 10 x 30 blown fiber furnace filter, shown in the pics, cut it down to 2pc 9 x 13 and you have two replacement filters for under $5. Helps to reduce noise and will reduce corrosion caused by and organic dust and debris. (organic-anything with a carbon atom) doesn't seem to affect air flow at all, (zero restriction). Remove metal wire fan guard and replace with filter, use the same screws. (ITS Actually Pretty Sexy Once You Get It Installed, It Adds To a Mechanical Appearance) It has a very valuable function in increasing the machines lifespan.