Inside the Vapor Eliminator located on the left side of the INOV8 burner is a 10 micron rayon filter. It can be purchased through General Filter or Unifilter, but is readily available from INOV8. We advise always keeping at least one on hand. This filter protects the pump shaft from the wear metals that are naturally in motor oil. As the oil is being heated at four feet per second around the oil heater it passes through the pump and through this filter. The INOV8 burner is the only one that filters hot oil so any charring from the heating process is captured in this filter. The filter can be used with most types of petroleum and vegetable oil but some solvents dissolve the filter. If your oil contains questionable solvents, it is advised that you test your oil by placing the filter into a small container for 24 hours. If the filter distorts during that time it is not compatible with your oil and you should order the optional filter for bio-fuels, p/n 30466. That filter is also 10 microns but made of wool fibers.