The first level of indoor air quality (IAQ) is the filter. This is the step that removes particles from the air by pulling the air through an element, usually paper, to grab the impurities. The rating of a filter shows how it performs. The Minimum Efficiency Rating Value (MERV) scale starts at 0 and maxes out at 21.
Air Purifiers are a compliment to air filters. They are designed to eradicate any impurities that pass through the filter. The UV light in an air purifier will change the DNA structure of the organism not allowing it to replicate. This will kill it in that it can not grow any additional cells.
Some believe that cleaning air ducts is not necessary. But if cleanliness’ is important, then you need to get any potential food source for bacteria out of our home. Check out this cheap and quick video of the inside of duct work as its being cleaned. There are different types of duct cleaning that range from a simple vacuum, to an agitation method such as a whip, a spinner ball and even a brush. All methods have their positive and negatives but any method done thoroughly will result in a clean duct system. If a simple duct cleaning does not get the air distribution system clean, consider replacing the duct work.
The next stage of clean air is to seal all of the joints in the duct work. Why is this important? To keep the ducts clean requires that all the air pass through the filter and air purifier. The return that is not sealed will suck in contaminates from a crawl space, wall void or attic. There are a couple of methods of sealing ducts from metal foil tape, to mastic or a think paint, to new air based sealants like AeroSeal that pressurize the ductwork to find the leaks and slowly ‘glue’ the hole shut.