"Filters are an integral component of every HVAC unit and proper care needs to be taken of these filters. However, there are different kinds of filters which are used in furnaces. They are the following:Fiberglass filters: This is the most common filter that is used in furnaces. They are less expensive and less effective at the same time. They can only protect the HVAC component and are not able to improve the indoor air quality. These filters should be changed at regular intervals and have a MERV rating of 1 and 4.Pleated Filters: These filters are made of cotton and polyester and they can hold back smaller particles like spores and mites. They have a MERV rating of 6 and require a timely replacement.Washable filters are those furnace filters which can be reused after washing. These filters require high maintenance because if not washed at the right time it will lead to clogging.Electrostatic filters: There are two kinds, one is the permanent and the other is the disposable. Both these filters use self-charging cotton or paper fibers in order to attract smaller particles. The permanent electrostatic filters have a MERV rating of 8 and the disposable one is rated 10.Lastly, there is the high efficiency pleated filters. They have a MERV rating between 14 and 16 and can hold back even the smallest of particles. These filters are mostly used in hospitals."