The Minimum Efficiency Reporting Value (MERV) rating of an air filter is a measure of how effectively it prevents dust and other contaminants from entering the air stream. MERV values range from 1 to 16, with higher ratings trapping small particles more effectively. While the highest MERV ratings are the most effective for air quality, they can also have some drawbacks. A higher MERV rating means higher resistance, which translates to less airflow.
This can lead to reduced comfort in the hottest and coldest climates, as your system may not be able to provide enough heating or cooling to your home. It's also important to remember to change the filter regularly, as a highly effective air filter can quickly become clogged with contaminants and increase the pressure drop. Using an air filter with a MERV rating higher than that recommended by the manufacturer of your boiler or air conditioner can also affect its performance. If exceptionally high filtration is desired (above MERV 1), separate air filtration equipment with a HEPA filter may be necessary.
HEPA filters trap the smallest particles at a higher rate than even MERV 16 and are generally used in surgical operating rooms, clean rooms and other settings that require absolute cleaning. If the furnace is located where the owner can access it to replace the filter and where the location of the furnace allows the width of the return duct to be increased, then it may be possible to install higher MERV filters. However, if you want to use pleated filters and taller MERV filters, then you should have a professional install a 5- to 6-inch media filter. Vacuum bags used as inserts for masks should be avoided, as they contain fiberglass which is very bad for breathing. The best option for high filtration would be an air filter with a MERV value of 16 which can filter 95%. There's also a YouTube video showing how to make your own N95 mask with a filter.
