MERV and 3M Performance Rating
MERV stands for Minimum Efficiency Reporting Value and is a number from 1 to 12, produced from a test designed by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). The MERV rating is intended to help people compare filters and a higher MERV rating indicates better filter performance. The 3M Filtrete Ultra Allergen filter is rated MERV 11. 3M also produces ratings which focuses on a filter's performance at capturing the smallest airborne particles measured in the ASHRAE test. 3M uses particle data between 0.3 and 1 micron in size to calculate a Microparticle Performance Rating or MPR. The 3M Filtrete Ultra Allergen filter receives an MPR of 1250.

Recommended replacement: at least once every three months.
It is important to remember to change your Filtrete filter on a regular basis. While Filtrete filters are designed to last up to three months, certain conditions in your home will significantly add particles to the air. This will cause the filter to capture more particles than usual, shortening its life to less than three months or reducing the effectiveness of the filter to capture particles. These conditions include: Dirty ductwork, construction work, sanding projects, pets, burning candles, tobacco smoke and fireplace/wood-burning stove smoke. In addition, running your furnace or air conditioning fan continuously will help clean the air in your home but could shorten the life of the filter. So, if you use a Filtrete filter under these conditions, it could begin to restrict airflow, especially in energy efficient furnace and air conditioning systems. In these cases, change the filter more frequently.