When it comes to air filters, the Minimum Efficiency Report Value (MERV) rating is a key indicator of the filter's ability to capture larger particles between 0.3 and 10 microns (µm). The higher the MERV rating, the greater the resistance, and the more contaminants it can trap from the air stream. This helps protect your heating and cooling equipment from damage, as well as improve indoor air quality. In addition to MERV ratings, some filter brands and retailers use alternative scales, such as Home Depot's Air Filter Performance Rating System (FPR) or the MPR (on 3M Filtrete air filters).
Many manufacturers also say that their HVAC filters are “allergen filters” (or something similar). But they are usually only filters with a rating of at least MERV 11, the classification in which the filters begin to trap most of the particles that are the size of common allergens. HEPA (High Efficiency Particulate Air) is a much stricter standard than MERV. Because HEPA filters have such tight filtration, they tend to restrict airflow so much that they are not practical for most residential forced air systems.
HEPA filters, on the other hand, are commonly used in air purifiers and vacuum cleaners. When replacing an existing filter, it is important to find the right size. HVAC filters are usually located in a slot next to the boiler or air controller. If there are gaps around the sides or it doesn't line up with any joints, it might not be the right size.
If you're reading this in the hardware store's filter aisle, don't bother trying to guess the size, there are at least a dozen common dimensions and you're likely to choose incorrectly. The models that score the highest in airflow tests also tend to have lower MERV ratings and cost less, although they don't perform as well in particle capture tests. If you want to be sure how much airflow your air conditioning system requires to work properly, you'll need to measure static pressure. Your HVAC professional would install a small cabinet next to your oven or air controller (on the air intake side) to hold the thicker filter.
The job should only cost hundreds (not thousands) of dollars. A MERV 11 filter only needs to stop 20% of particles smaller than 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 smaller than 0.3 microns, and a MERV 13 only needs to stop half. Compared to the cheapest basic filters available, medium-efficiency MERV filters can greatly reduce airborne dust, mold spores, pollen, and even smoke, and doing so can help alleviate respiratory illnesses. Some sources have stated that the scale achieves the MERV 20, but the test standard has been updated to clarify that the MERV 16 is the maximum.
If you want to disinfect your filter without using harsh chemicals, you could very well be creating some strange, weird and fun chemicals unless you're just washing cotton; so I would only use sunlight to disinfect them, even that could break down some of the higher Merv filters a little and release an unintentional, perhaps dangerous chemical. De-gassing an activated carbon filter with a high Merv content could be your best option between you and any other exotic chemical action you're doing. The Merv 16 would be your best bet since it will filter 95%. There's even a YouTube video showing how to make your own N95 with a Merv 16 filter. When it comes down to it, choosing an air filter with an appropriate MERV rating is essential for protecting your health and home from airborne contaminants.
It's important to understand what each rating means so that you can make an informed decision when selecting an air filter for your home or business.