How to Choose an Air Filter by Particle Size?​

Created By RISC | 11 months ago

Last modified date : 11 months ago

The PM2.5 problem remains a chronic issue since the causes—vehicle exhaust, industrial pollution, agricultural burn-off, including from neighboring countries—have not yet been solved. Particles in the air reach unhealthy levels during the winter with still weather and calm wind.​

If you have to go outside, wear a mask. Also, in accordance with US National Institute for Occupational Safety and Health (NIOSH) guidelines, masks help protect against PM2.5 particles (dust no bigger than 2.5 microns). A N95 mask is named with N for non-oil-resistant and can filter at least 95% of particles less than 0.3 microns.​

But are we safe inside with air conditioning and closed doors and windows?​

It depends on building leaks. But the more closed a building is, the more likely that it will accumulative pollutants, such as CO2 from breathing or volatile organic compounds (VOCs) from household cleaning products, perfumes, furniture, or building materials. If these pollutants rise above standard levels, the health of the residents may suffer.​

A Fresh Air Unit (FAU) system, Outdoor Air Unit (OAU), or Energy Recovery Ventilator (ERV) can help deal with PM2.5 indoors. To prevent PM2.5 from entering the building, the system exchanges indoor air pollutants and filters outdoor air before bringing it in.​

There are many different types of air filters available depending on the type of pollution. There are several different standards for particle filters based on their properties and filtration efficiency per particle size. The ASHRAE 52.2-1999 standard is referred to by some manufacturers. The American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) is an American air conditioning and refrigeration engineering society that categorizes filtering levels into MERV (Minimum Efficiency Reporting Value) levels ranging from MERV1 to MERV16.​

Choose an air filter with a MERV 13 or higher to filter PM2.5 particles or particles smaller than 2.5 microns. The ability to filter will improve as the MERV increases.​

Furthermore, some manufacturers may refer to the EN779:2012 standard, which is a 2012 revision of the European Standard. Air filters are classified as coarse or fine filters under European standards. The weight of the particles that the air filter can hold is used to classify the G1-G4 grade filters or coarse filters. The efficiency of fine filters in grades M5-F9 in filtering particles with a diameter of 0.4 microns is measured. In comparison to MERV values of 13 or higher for PM2.5 filtering, choose a filter at level F7 or higher from the table below.​

Since we know the level of particle filtration, we can select and purchase appropriate air filters to ensure the good health of building occupants.​

Story by Panpisu Julpanwattana, Senior Sustainable Designer and TREES-A Specialist, RISC