If I asked you to rate the quality of the air in the homes you build, how would it score? Would that rating be based on anything more than a guess? Very few of us know if our homes are filled with harmful gases or lung-damaging particulates. There are two primary sources of this invisible pollution soup. The first is comprised of gaseous pollutants from complex chemicals that originate in all the stuff we use. Some of these gases are toxic to start with, but most are relatively harmless in small amounts until they mix with each other. Because there is little data on the effects of these chemicals on health, we must assume these compounds should be diluted and ventilated or preferably eliminated before we start. The other key ingredient is particulate matter from plants, animals, shoes, carpet, cooking, and other sources. Many are unaware of these hazards until they cause us to sneeze or there’s a detectable odor.

As discussed in previous issues, it is imperative that homes have both controlled and distributed ventilation as well as good filtration. We are covering the particulate side of this equation here.

So, how do we manage the invisible? One tool, in combination with good ventilation, is an active air filtration system, measured by filter performance. Here are five criteria for evaluating and comparing active filtration systems.

Particle Removal

Before considering the merits of different types of filters, it’s important to understand the problem: Just how big and how numerous are the particles floating in the air inside most homes?

Dust particle size is typically measured in microns or micrometers, which are 0.0001 of a centimeter. In bright light, a 10-micron particle is just visible to the naked eye. The dust particles dancing in a sunbeam are probably larger than 10 microns in diameter, as are pollen, mold spores, and dust mites. Visible particles account for less than 2% of the particles floating around a typical house; the other 500,000 to 1 million particles per cubic foot are much smaller—usually in the 0.3- to 1-micron size range. These may stay suspended in the air for hours, days, or weeks at a time.