Answered: What is a MERV Rating and Why Does It Matter?

Airborne particles like dust, allergens and pollutants can reduce your home’s indoor air quality. Your HVAC system includes an air filter to try and trap these particles, preventing them from circulating through the system. But there are lots of different brands and filter types, so which filter is best? Finding out what works for you is easier with the MERV rating system. Developed in 1987 by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), MERV stands for Minimum Efficiency Reporting Value. With a range from 1-20, you can directly compare available air filters.

The highest MERV ranking of 20 means that an air filter will capture the largest percentage of airborne debris. Depending on what contaminants are present, this can vastly improve your indoor air quality. At the same time, the lowest rating means a filter is less effective, especially with smaller substances like bacteria and mold spores. By checking the MERV rating, you can get a good idea of how a specific air filter will perform.

Do I Need a Specific MERV Rating? If So, Which One?

Generally speaking, Simons Heating & Cooling recommends that your HVAC system’s air filter should have a MERV rating between 6 and 8. This strikes a great balance between air quality, efficiency and overall comfort. But if someone in your family has health concerns such as allergies, you may want to look for a high-efficiency filter with a rating of 11 or higher. When it comes to the average household, a rating of 8 is usually sufficient. For comparison, a filter with a MERV rating as high as 16 is usually reserved for specialized facilities like hospitals.

How to Determine Your Furnace’s MERV Rating

The air filter is usually found in the furnace’s air handler, which is responsible for circulating climate control throughout the airducts. To determine the appropriate MERV rating of your furnace filter, refer to the system manual. You can also determine the size of the air filter by pulling out the current filter. The dimensions should be printed on the frame.

MERV filters with ratings between 1-4 are flat instead of pleated, so there is less surface area for trapping particles. On average, they only capture particles larger than 10 microns in size such as hair, pollen and dust. MERV filters rated 5-8 can capture particles as small as 3 microns in size, which includes mold spores and animal dander.

Filters rated 9-12 start to rival what are known as true high-efficiency particulate air or HEPA filters. At this degree of efficiency, the filter can remove particles from your indoor air that are hazardous to your health. HEPA and similar filters are ideal for people with COPD, allergies, asthma and other respiratory conditions. At the highest end of the scale, ratings of 13-20 are found in commercial HVAC systems, such as those found in manufacturing plants or hospitals.

Does a higher MERV rating restrict airflow from your furnace?

Generally, filters with higher MERV ratings may start to reduce airflow. At the same time, there are other factors at play. The size of the filter, how often the filter is replaced and the specific materials used in the filter’s design will all have an impact. Restricted airflow can decrease comfort while increasing your energy costs, since the system has to run longer than normal.

If the MERV rating is too high for your model of furnace or air handler, airflow will likely be reduced. Ultimately it depends on the quality and strength of the furnace itself. Don’t forget that a clogged air filter, no matter how efficient, will also reduce airflow.

Does a MERV rating have an impact on the indoor air quality of my home?

Yes. The higher the MERV rating, the fewer air pollutants can pass through the filter and the better your indoor air quality will be. Using an air filter with a MERV rating of 13 or higher can filter out as much as 85% of indoor pollution.

You may want to consider converting to a filter with a higher MERV rating if you’re concerned about your home’s indoor air quality and how it impacts your health. With comprehensive training and years of experience, a professional HVAC technician can make a big difference for your home’s indoor air quality.

 What Is the MERV Rating of a HEPA Filter?

A HEPA filter is typically made of small plastic fibers (polypropylene), fiberglass or borosilicate glass fibers. In the right setup, these filters remove up to 99.9% of indoor pollutants. They are tested using particulate matter 0.3-microns in size, as these are the most difficult particles for a HEPA filter to catch. HEPA filters will be the most efficient option to capture the smallest-sized particles, like viruses (which are on average 0.1 microns).

If you have more questions about the your furnace or its air filter, contact the air quality experts at Simons Heating & Cooling. We’ll do whatever we can to help you make the best choice for you.