Resizing a Furnace Filter

My wife picked up a high-end Honeywell furnace filter at a garage sale recently for two dollars. That's not a bad price considering what the things retail for^[1].

There's just one little problem -- the filter is 20"x20"x1"^[2], and our furnace takes 16"x20"x1"^[2] filters.

Now, how hard can it be to resize one of these things? Let's see what I can do with a straightedge and a sharp utility knife.

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That went fairly well. Here's a shot of the cut off end of the filter, and of how I'm trimming the glue off the end cap that I've peeled/sliced away.

The filter is well-constructed of quite tough materials, and the manufacturer didn't scrimp on glue.

What I have in mind is to reattach the end cap with hot-melt glue. I should end up with a reasonable facsimile of a 16"x20" filter.

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That turned out not too shabby at all. Here's a close-up view of one end of the reattached cap.



So, should you come across an oversize filter, or a whole truckload of oversize filters at a really good price, snap them up -- they're not difficult to modify to fit.

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[1] I can't seem to find a price for this exact filter, but from what I've seen, the retail price of these things is outrageous.

I'll grant that they're well made of excellent materials, and I have no reason to dispute what's claimed for the things, but just how well must I be protected from every conceivable pollutant in this world to go on living in it? How did the human race ever get past cave-dwelling without Honeywell cave-fire filters to keep it healthy?

The paper wrapper that was on the filter tells me that, "This filter cleans the air of: pollen, household dust, auto emissions, mold spores, animal dander, bacteria, particles that can carry viruses [!?], smog particles." Or, to put it another way, possibly, "Be afraid! Spend lots of money on our filters and we'll protect you.

[2] The nominal dimensions of these filters are just that -- nominal; they're all made slightly undersize so they'll fit easily in their racks.

The Honeywell unit states actual dimensions of 19 5/8"x19 5/8"x13/16". The mesh filter I have is similarly undersize, though it doesn't state actual dimensions; it just gives a metric equivalent of its nominal dimensions (406mm x 508mm x 25mm).

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