Efficient and effective filtration is one of the foundational pillars of any well-designed building HVAC system. With regard to air filters and cleaners, efficiency is a term that refers to the ability of a collecting medium to capture contaminants from the airstream that pass through it. The effectiveness of an air cleaner refers to its ability to reduce particulate concentrations in a space. The U.S. Environmental Protection Agency (EPA) tells us, “It should be noted that expected removal efficiencies for air-cleaning devices are not the same as the effectiveness of the unit in actual use. Efficiency only measures the percent removal of contaminants in the air that flows through the air-cleaning device. Effectiveness in use depends on how much of the interior air actually goes through the unit in a given time period”1.
If space contaminants in the air do not pass through the air filter that is tasked with their removal, the effectiveness (actual contaminants removed) may be less than expected regardless of the filter’s rated efficiency. Simply put, a filter described as very efficient may not be all that effective in actual use.