The indoor air in your home circulates through your homes return air duct, into the cooling/heating system and back into your living space. The air is full of little particles from both manmade and natural sources. Pollen, dander, mold, tobacco smoke along with some select viruses and bacteria. Most of these settle and appear as dust in your home. While most of these particles settle some can become airborne again with the smallest disturbance. Having an Air purifier installed near your furnace or by your air handler of your home might help remove some of the airborne particles that are circulating through your home. Having these particles removed from your home keeps equipment clean, but most importantly this removers the particles from the air that you breath.