Which grade of HEPA filter you need?

High efficiency particulate air (HEPA), originally called high-efficiency particulate absorber (Sometimes called high-efficiency particulate arresting / high-efficiency particulate arrestance, is a type of air filter. Satisfied the HEPA standard such as set by the United States Department of Energy (DOE), the filters have many applications including medical facilities, automobiles, aircraft and homes.

To qualify as HEPA by US government standards, an air filter must remove (from the air that passes through 99.97% of particles that have a size of 0.3µm. The air space between HEPA filter fibres is typically much greater than 0.3 μm. HEPA filters are designed to arrest very fine particles effectively, but they do not filter out gasses and odor molecules. Circumstances requiring filtration of volatile organic compounds, chemical vapors, cigarette, pet, and/or flatulence odors call for the use of an activated carbon (charcoal) or other type of filter.

HEPA filters, as defined by the United States Department of Energy (DOE) standard adopted by most American industries, remove at least 99.97% of airborne particles 0.3 micrometers (µm) in diameter. The filter's minimal resistance to airflow, or pressure drop, is usually specified around 300 Pascals (0.044 psi) at its nominal volumetric flow rate. The specification usually used in the European Union is the European Norm EN 1822:2009. The classes of HEPA filters are from E10 to U17.