How Are Furnace Filters Measured?

Filter Size

• The physical size of your furnace filter is very important. If you have a filter that is too large, it will not fit in your furnace, and one that is too small will not do the job properly. To find the correct size, look on the existing filter or in your furnace manual.

Filter Quality

• Different furnace filters will operate at different levels of efficiency when it comes to removing such particles as dust, mites and allergens. The most common measurement of efficiency is the MERV rating.

MERV Rating

• The MERV rating of a furnace filter ranges from 1 to 16, with the larger numbers being more efficient and able to filter out more types of particles. Filters rated between 5 and 8 are a good choice for homes, while filters with a rating above 13 are used in hospitals, according to Furnace Filter Care.

Filter Replacement

• When it comes to furnace filters with high MERV ratings, the mesh that is used to trap particles is very fine. If they are not replaced as recommended by the manufacturer, they can cause performance and air flow problems.

Electrostatic Air Filters

• An electrostatic air filter is a special type that does not have a MERV rating. These use static electricity to remove particles from the air, rather than a physical barrier.