Allergy air filters for sale are tested for keeping out some of the most common particles before being released in the market. Among these particles are bacteria, dust, pet dander, pollen, textile fibers, and tobacco smoke. Many home systems can block these particles with a filter rated MERV 7 to 12, so higher one may not necessary.
The above poses an important question though: Which filter among those with MERV ratings from 7 to 12 should be chosen? Buyers can choose one that filters out particles yet allows fast airflow within the area. A rule of thumb is to grant at least 1.25 square feet of filter area for every ton of air conditioning.
Ideally, filters with higher MERV ratings need to be replaced every three months. Doing so minimizes restricted airflow that allows furnaces, air conditioners, or other HVAC systems to work more efficiently. For people whose furnaces have heat sensors, these shut down if their heat exchangers get too hot due to restricted airflow.