What's the Difference Between HEPA and MERV Filters?

A HEPA filter is the top of the line when it comes to air filters, with a rating equivalent to a MERV 17 or higher. A HEPA filter with a MERV 17 rating will trap 99.97% of air particles that are 0.3 microns in size, and even more of particles smaller or larger than that size. The difference between HEPA and MERV filters lies in the size of the particles they can capture. HEPA filters capture 99.7% of particles that are 0.3 microns in size, while MERV 13 filters can only capture up to 75% of 0.3 micron particles. To understand which MERV filter might be best for you, it's important to know the difference between MERV and HEPA filters. Air filters are tested by measuring dust spots that contain some fine dust, powdered carbon, and some cotton filters.

This means that a filter with a MERV rating of 14 can remove volatile organic compounds, while another filter with the same rating may not be able to achieve this same level of filtration. The following table summarizes the average arrest and applications of filters along the MERV scale, as well as the typical particle size for which they are used:

• MERV 1-4: Used for pre-filtering large particles such as dust, pollen, and mold spores.
• MERV 5-8: Used for general air filtration, such as in homes and offices.
• MERV 9-12: Used for capturing smaller particles such as smoke, bacteria, and viruses.
• MERV 13-16: Used for capturing very small particles such as smoke, bacteria, and viruses.

Considering the threat posed by the spread of COVID-19 and other germs, changing a building's air filter to a HEPA is a much more effective step than simply a MERV 13, considering the small size of the virus (0.06 to 0.12 microns); the more efficient the filter, the better. HEPA filters are the most efficient for residential or commercial use, followed by MERV 13-16 filters. However, HEPA filters have a significant drawback - they cause a greater pressure drop than MERV-rated filters. This means that if you were to use the dust spot test used in HEPA filters on a MERV 16 filter that uses the ASHRAE test protocol, the MERV 16 filter would only have an efficiency of approximately 50%.A filter with a high MERV rating is especially recommended for households with allergic and asthmatic people. The Minimum Efficiency Reporting Value (MERV) is an effectiveness scale for air filters developed by ASHRAE in 1987 that measures the size of particles that can pass through them. In conclusion, HEPA filters are more efficient than MERV-rated filters not because they don't meet the requirements for MERV testing and classification, but because the manufacturing process for HEPA filters already guarantees a higher rating than MERV.