Before we discuss ventilation, it is important to know why ventilation is important. Do we really need these additional mechanical devices in our homes? Yes. Haven’t we been OK without them for decades? Yes and no. We address many of the major contaminants found in our homes, including PM2.5, formaldehyde, acrolein, nitrogen dioxide, and moisture. It is important to keep contaminants out of the house (source control) and manage those that are generated in the house by ventilating and filtering the air. This is the first video of two.