Mechanical filters are the most trusted and widely used tools for cleaning the air. They work like sieves—capturing particles as air passes through. Two main rating systems help us understand how well they work: HEPA and MERV.

HEPA filters (High-Efficiency Particulate Air) are the gold standard. They capture at least 99.97% of particles down to 0.3 microns in size—which includes mold spores, pollen, pet dander, bacteria, and some viruses. You’ll find HEPA filters in high-end portable purifiers and in some vacuums and HVAC systems (though retrofitting HEPA into HVAC requires professional adjustment).

MERV filters (Minimum Efficiency Reporting Value) are used mostly in HVAC systems and range from MERV 1 to MERV 16. The higher the number, the finer the particles the filter can capture. For most homes—especially those with health concerns—a MERV 13 or higher is recommended, as it removes fine particles like smoke, bacteria, and allergens.

Mechanical filters are safe, don’t produce byproducts, and provide consistent performance when replaced regularly. Their only downside? You have to change them on schedule to keep them working effectively.