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Pleated Furnace Filter Direction

Pleated Furnace Filter Direction
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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 pleated-furnace-filter-directionit 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 pleated-filter-cardboard-frameit 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.


About the author: Don has been working in the HVAC industry for more than 25 years and shares his experience and knowledge on this site. If you find the information presented here helpful please share with your friends.

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  • Karen Harris

    Thanks for answering my email. The cardboard X made me so nervous. I was praying I didn’t install the filter incorrectly. I also called Home Depot around 7 yesterday morning. They, too, told me I was installing the filter correctly. I know I emailed you around 2 a.m., and I was so nervous about the installation. I said Home Depot opens at 7, so their answer will hold me until I hear from you. I love these filter. Plus, they are good for 3 month. They product efficiency and money efficient. Thank you again.

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