WHAT SIZE PARTICLE SHOULD A FURNACE AIR FILTER REMOVE?
A good allergy and asthma filter should remove both large and small particles. A typical furnace has a one inch thick rough filter which can remove most of the large particles. Also available are one inch pleated filters or one inch plastic mesh electrostatic filters, both of which can improve efficiency. All these filters are affordable, but none is very effective at capturing small particles. To remove small particles, you could install on your furnace a four inch deep slot for either a pleated HEPA or an electronic filter. A HEPA filter can move up to 98% of the small particles in the air down to 0.3 microns in size. Electronic filters can remove even smaller particles, but are not as good at removing large particles, and may require weekly cleaning to maintain peak performance (Webmaster: CMHC has an interesting study on this topic 2008). Both of these filters can quickly become clogged with large particles, so it is best to install a rough filter in front of them to screen out mos
