Subaru Forester Cabin Air Filter General DIY

Replace the Cabin Air Filter in a Subaru Forester

Works For:
1997, 1998, 1999, 2000, 2001, 2002, 2003, 2004,  2005, 2006, 2007, 2008, 2009, 2010, 2011 Subaru Forester Models


Hi Everyone, I’m new to posting on this forum but I’ve been reading various posts and learning so much from everyone’s input here. I’m a new, proud owner of a 2003 Forester XS premium that I bought about 3 weeks ago. I’ve already done a little bit of work on it using threads from this forum as well as’s forum and some links to other Subie forums. I wanted to give back to the forum for already giving me so much useful information and saving me money by doing things myself.

This weekend I did some reading about DIY cabin air filters and used the ideas from other threads on making a homemade filter. I took pictures of the steps I followed on how I made my filter.

As I mentioned, this was for a 2003 forester, but the steps can probably be used for other model years as well.

All I needed for this project was a 90-degree piece of aluminum ceiling tile rail, the type that goes along the wall. (the shortest length that was at the store was 12 feet, good thing I had to buy aviation snips while I was at the store so I cut cut it in half to fit in the car).

Straight Aviation Cutters or tin snips for trimming the railing.

A furnace filter to cut to size.

1) Measure the dimensions of of the filter housing, I measured mine at about 7 5/8″ x 8 5/8″.

2) Mark the railing at 7 5/8″ from the end, then 8 5/8″ from that mark, then 7 5/8″ from that mark, then mark another 8 5/8″ from there, and finally mark about 2″ or so and cut the rail to that length. So the total length for me was about 34 1/2″. Make sure to cut on the same side of the rail.

3) At each mark I cut straight/perpendicular into the metal on one side.

4) Then make two more cuts into the rail making a “V” shape with the point of the “V” where the first straight/perpendicular cut was made.

5) Bend and twist off each triangle, but BE CAREFUL NOT TO CUT YOURSELF. The metal is sharp. It should look like this:

6) Then bend the rail inward overlapping the inner rail. This will for the bottom of the filter tray.

It will start for look like this:

7) When you get to the last 2″ segment, bend it so it’s outside the other end.

8) This is the TRICKY PART. I messed this up the first time and had to make another one, but it’s okay because the piece of metal is more than long enough. What you want to do is cut a rectangular piece out of the inside part that overlaps where the short end extends. Remove that piece and mark on the short end where that cut out is.

9) Cut along those lines but DO NOT REMOVE THAT SECTION. Fold that section up into the space previously made. This will hold the filter frame together.

10) Now make some adjustments to the corners so it’s square and then check to make sure it fits into the cabin filter housing. With my dimensions it was a perfect fit, but I think just marginally too big, but it did fit.

11) Take the furnace filter and mark the direction of airflow along the cardboard edge so in the future you know which way the air flows. Then hold then I held the filter frame up to the filter and guessed the size to cut. I used the tin snips to trim the wire to size, but a good pair of scissors can cut through easily enough. I also peeled off as much of the cardboard around the edge to allow more air to pass through.

12) Place the filter in the frame and it should look like this:

Now go and put it in your Subie and enjoy fresh air!

The furnace filter you use can be any kind, I used a slightly more expensive Filterete with hypoallergenic filtering, hoping for cleaner air.


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