Understanding MERV Ratings and Their Impact on Air Filtration

As crises such as COVID-19 and wildfires impact the country, chances are more clients are asking about indoor air, health and safety in the home. Many NAHB members are already using various construction techniques, such as active radon mitigation systems and installing low- or no-volatile organic compound (VOC) materials, to set themselves apart in the market and improve indoor air quality (IAQ) in the homes that they build. How can you effectively talk about air filtration and ventilation, particularly when these issues are top of mind for customers during the pandemic? To start, it is important to understand how the Minimum Efficiency Reporting Value (MERV) rating system for air filters works. MERV ratings range from 1 to 20, with 1 being minimal filtration and 20 being the highest efficiency and maximum filtration on the scale. Ratings are determined by ANSI/ASHRAE Standard 52.2. Air filters work to remove particulate matter (PM) and other irritants from the air. Understanding the differences between MERV ratings is important, as the highest rating doesn't necessarily mean it’s the best fit for your specific project. For example, you should make sure that the HVAC system can handle filters with higher MERV ratings, as the airflow could be compromised because of higher filtration. A higher-rated MERV filter will also require the HVAC system to use more energy to pull the air through. Indoor airPLUS' construction specifications provide a good starting point. For air inlets, the Environmental Protection Agency (EPA) recommends using a MERV 13 filter or higher to curtail outdoor particles from entering the home. For central forced-air HVAC systems, Indoor airPLUS requires installation of MERV 8 or higher filters and recommends putting in filters rated at MERV 13 or higher. MERV-rated air filters offer a variety of benefits across the scale. On the higher efficiency end, MERV 11 and higher filter out smaller particles that range in size from .3 – 1.0 microns in diameter. Irritants such as tobacco smoke or smog fall in this category. If a home has a filter less than MERV 11, these potential allergens have a higher chance of being more prevalent in the home and could affect the comfort of your customers by prompting an allergy attack or triggering asthmatic occupants. Particles ranging from 1.0 to 3.0 microns (e.g., lead dust, car emissions) can be filtered out by MERV filters rated above 8. Filters rated at MERV 8 and below have the ability to filter out larger particles, such as those ranging from 3.0 to 10.0 microns in diameter (e.g., hair spray, mold spores). Communicating with your HVAC contractor early in your design process is essential for determining what types of air filters the system will use. Beyond working with your HVAC professionals, you can also take steps to educate your customers about how your newly constructed home takes steps to improve IAQ, and therefore, their health and comfort. Consider using different filter types in your model homes and demonstrate the differences as a discussion point to talk about healthier indoor air. To stay current on the high-performance residential building sector with tips on water efficiency, energy efficiency, indoor air quality, and other building science strategies, follow NAHB's Sustainability and Green Building team on Twitter.