Filtrete Ultra Allergen Reduction Air Filter, 1500 MPR (Previously 1250), 20-inch By 20-inch By 1-inch, Case of 12

1500 MPR and 1250 MPR may be mixed in every case. The 1250 MPR was the original Ultra Allergen filter and with continual testing of the products, the filter was under rated and 3M now claims a 1500 MPR. Both the 1250 and 1500 filters offer the same performance. There have been no changes to the filter, just the MPR # has been changed. Filtrete Ultra Allergen Reduction Filter attracts and captures pollen, mold spores, dust mite debris, smoke, pet dander, household dust, smog, bacteria, and particles that can carry viruses. How often should I change my filter? For cleaner air, this filter should be changed at least every three months. Changing your filter more frequently makes your system run more efficiently. 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, fireplace and wood-burning stove smoke. Also, running your furnace or air conditioning fan continuously will help clean the air in your home but could further 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. If these conditions exist, change your filter more frequently