I bought a package of 3 pleated air filters from Flanders. I am not sure how to install them. One side is plain white pleated and the other side is plain white pleated with a X of cardboard. Which side goes toward the furnace? What is the proper furnace filter direction?
As discussed in previous articles, there are many different types of filters and often it is difficult to determine which way a furnace filter should be installed.
The filter type that generates the most questions regarding which way it should be installed, is the pleated air filter. These filters also happen the be the most popular air filters for home owners. Because of this there are many manufacturers competing for market share and therefore many different designs.
To increase the durability of pleated air filters, manufacturers often extend the cardboard frame across the face of the filter in the form of an X or strips. This enables to filter to maintain it’s shape and prevents it from collapsing under the strain exerted on it when air is passing through it.
If , as in this case, there is only one side of the filter that has cardboard across the face. That side should be facing the furnace.
p.s. Most manufacturers of pleated air filters stamp an arrow on the frame of the filter to indicate direction. The arrow should point toward the furnace.