Filters with a Merv rating of 17 to 20 are rarely necessary 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. The AC coil inside or near your oven or air controller cools down significantly as it draws heat from the space and pumps it out. Low airflow can cause the coil to cool below 32°F, resulting in moisture in the air freezing and the coil becoming encased in ice.
This prevents your air conditioning system from doing its job. The goal of using a MERV 12 filter or higher is to improve indoor air quality (IAQ) by removing more pollutants from the air, which is especially beneficial for those with allergies, asthma, COPD, etc. If you're looking for an alternative to a high MERV filter for use in ovens or air conditioners, you may want to research air purifiers. A Merv 11 filter has a higher efficiency rating and can capture finer particles.
In general, a filter with a higher MERV rating will reduce airflow. However, there are many other factors at play, such as the size of the filter and the type of fan motor in your HVAC system. Higher MERV ratings are more effective and improve air quality, but they are also more expensive. Plus, taller doesn't always mean better for homeowners.
MERV ratings greater than 16 are typically used in specialized commercial environments where air filtration is essential, such as hospitals. In general, filters with a MERV 8 rating or higher should be used in residential HVAC systems. The American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE) now recommends using MERV-13 filters (ASHRAE Position Paper on Infectious Aerosols) as a measure to provide cleaner air in non-sanitary facilities. Technology for HVAC units has progressed since then, and most modern units in recent years should be able to have a MERV 8 filter at least. Although Merv 13 is suggested by ASHRAE, it may not be the most efficient option for some residential HVAC systems. Meanwhile, air filters with a MERV 14 rating or higher are designed for commercial HVAC systems that can handle the coarsest filter material. Finally, I suggest that if you feel that a high merv filter would provide peace of mind, you should do so with the caveat that you should replace dirty filters often enough - this could be every week or two depending on the MERV rating, the effective area of the filter and the quantity of particles entering your home.
A MERV 11 filter only needs to stop 20% of particles at 0.3 to 1.0 microns (three to ten times larger than a COVID-19 particle), a MERV 12 only needs to stop 35% of particles below 0.3 microns, and a MERV 13 only needs to stop half. I also want to introduce an activated carbon filter with a Merv 8 rating as an option between you and any other exotic chemical action you have going on. Filters that are above 13 in their MERV rating can filter particles closer to the 0.3 micron size. The way HERS is done in California has for some time influenced outdoor air supply to be provided by a separate route from heating and cooling, since an uncontrolled CFI outdoor air inlet is not allowed to be sealed during the check for leaks in the duct.
