According to the National Air Duct Cleaners Association an average home collects as much as 40 pounds of dust, dirt and allergens in a year. This dirt contains about 40,000 dust mites and hosts unhealthy bacteria, mold and fungi. Air ducts are an ideal environment. Place the cone filters behind the air exhaust valvles to keep your air ducts clean and postpone air duct cleaning significantly. Read More
If you are not sure about the diameter of the air ducts then order the largest ones. The cone shaped filters can be customized easily.