Filters with a MERV rating of 17 to 20 are rarely needed in a residential home. A MERV rating of 13 to 16 is considered hospital-level air quality, so it's unlikely that your home will need more than that. However, using a filter with a higher MERV rating can reduce the airflow through the air conditioning system, which can cause the cold coil to freeze and restrict airflow completely. This can lead to more costly problems in the outdoor condenser coil. A MERV filter 13 is likely to be beneficial if the goal is to prevent droplets from passing through.
Air filters with MERV 13 or higher are recommended for those who prioritize air quality and may have to manage asthma, severe allergies, and other similar circumstances. Vacuum bags are not safe for masks since they contain fiberglass, which is very bad for breathing. However, MERV air filters are made of polyester and cotton and are safe for use in masks. When building a return, it is recommended to use two MERV filters 18x18 height side by side, giving you 648 SI of surface area for filtration.
A MERV 8 carbon filter will provide more than enough filtering of dust and allergens and will filter dozens of toxic gases that will pass directly through a MERV 13 filter. Filters with higher MERV ratings should be changed more frequently (at least every three months) to avoid restricted airflow that can cause the system to operate inefficiently or even damage it. Although the American Society of Heating, Cooling and Air Conditioning Engineers (ASHRAE) suggests MERV 13, it may not be the most efficient option for some residential HVAC systems.
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