When it comes to air filters, it is important to understand the nominal size, actual size, MERV rating, and type of filter. The nominal size of an air filter is the rounded value of its actual dimensions, which are used to label the filter. Generally, thicker air filters are better for filtration as they have more square feet to capture and retain air particles. For example, a 1-inch air filter may need to be changed every month, while a 4-inch air filter can last up to six months.
A 20x20x1 air filter actually measures 19-¾ x 19-¾ x ¾, which is known as an “undercut”. All filters 1 and 2 are trimmed by a quarter of an inch to leave some room and ensure that they fit the air return without being too big. This includes custom sizes, such as a 27 x 23 x 2 inch size. The Minimum Efficiency Reporting Value (MERV) rating lets you know what size air particles an air filter will trap. A higher rating means that the filter can trap smaller air particles.
When you buy an air filter online, it is important to know the nominal size (which is a round size often used to label the filter) and the actual size. You must also understand that air filters come in two sizes and that you cannot use a 4-inch-thick air filter in a system that's made for a 1-inch-thick filter. These filters will capture a large part of the particulates suspended in the air and improve indoor air quality without significantly increasing energy costs. It is also important to note that two 20x25x5-inch household filters made by two different manufacturers are not likely to be the same size. The American Society of Heating, Refrigerating, and Air Conditioning Engineers designed the MERV rating scale in 1987 to provide a more accurate picture of an air filter's capabilities. In conclusion, when selecting an air filter, it is essential to understand the nominal size, actual size, MERV rating, and type of filter.
Thicker filters tend to last longer and capture more dust particles than thinner filters. It is also important to note that two filters of the same nominal size may not be the same actual size.
