Air Systems Cleaning Specialist (ASCS) Practice Exam 2026 – Comprehensive All-in-One Guide for Exam Success

The correct answer is that HEPA filters are equivalent to a MERV rating of 17-20. HEPA, which stands for High-Efficiency Particulate Air, is designed to capture very small particles, including allergens, dust, and some bacteria, with a very high efficiency—typically over 99.97% for particles that are 0.3 microns in diameter. This exceptional filtration capability aligns with the higher end of the MERV scale, where ratings from 17 to 20 indicate filters that can effectively trap very fine particles.

Filters rated in lower MERV categories, such as MERV 1-4 or MERV 5-8, do not have the same level of efficiency and are primarily effective at trapping larger dust particles and contaminants, which is far less effective when it comes to smaller particles that may pose health risks. While filters classified under MERV 9-12 do provide good filtration for certain sizes of particles, they still fall short of the stringent requirements that define HEPA filtration standards. Therefore, recognizing that HEPA filters achieve their remarkable performance within the MERV 17-20 range is crucial for understanding their role in maintaining healthy indoor air quality.