18x30x1 (17.7 x 29.7) Filtrete 1250 Ultra Allergen Filter by 3M

My house uses forced air for heating. The disadvantage of such a system is that it distributes the dust in the air everywhere in the house. However, it is supposed to be possible to filter out the dust. Over the years, I have steadily increased the quality of the filter that I use for my forced air heating system. However, until now I have not noticed any obvious difference in my allergic reactions that seem to start with the heating season.

There are cats in my house. I have read that cat dander, tiny flakes of cat skin shed by the cats, is five times smaller than household dust particles. It stays in the air much longer than ordinary dust before it settles. Because of its small size it requires a more efficient filter to get it out of the air.

Until three years ago, I used of variety of filters with mixed results. However, then I started using the 3M Advanced Allergen Filters, the ones in the blue wrapper. These have a 3M Microparticle Performance Rating of 1500, and a MERV rating of 12.

MERV stands for Minimum Efficiency Reporting Value produced from a test designed by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE). A higher MERV rating indicates better filter performance.

3M uses particle data between 0.3 and 1.0 micron size to calculate a Microparticle Performance Rating or MPR. The higher the MPR, the better the filter. However, higher rated filters cost more.

Here are some of the Filtrete filters offered by 3M:

Dust & Pollen Filter, Microparticle Performance Rating 600,

MERV rating of 8

Micro Allergen Filter, Microparticle Performance Rating 1000,

MERV rating of 11

Ultra Allergen Filter, Microparticle Performance Rating 1250,

MERV rating of 11

Advanced Allergen Filter, Microparticle Performance Rating 1500,

MERV rating of 12

Ultimate Allergen Filter, Microparticle Performance Rating 1900,

MERV rating of 13.

The difference made by the Advanced filter was immediately obvious. My running nose stopped running. I assume that the new Advanced filters must be taking out more of the dust in the air including the cat dander. I have not noticed a change in the speed of the circulated air.

More recently, I have started using the newer Ultimate filter. It works better than the Advanced filter. The additional cost of the filter is worth it if you have allergies or pets. However, if you are happy with a lower-rated and lower-cost filter, then continue using that one.