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My furnace/AC was installed about three years ago. It uses 16" X 25" X 5" filters. The problem is when I try to find a replacement at my local home center: at Lowe's, Home Depot, (you name it), I found only 1" or 2" thick filters (mostly 3M Filtrete). I looked in many stores around my area, not just one. I also checked at my local Costco and Walmart but they have none: the associates told me that they didn't carry the filters anymore and that I may need to order them online.

So, the question is: Are 5" thick filters still in use and available? Is it an uncommon size filter? Or do the thin filters have better performance?

Additional Information: the filer that we are talking about is Honeywell FC100A1029.

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up vote 3 down vote accepted

The thicker the filter, the more area can be created within the filter by folding the filter materials into baffles. This creates a very high efficiency filter, but I don't think I've ever seen one this thick stocked in a store. I'm sure you could resize the opening for a thinner filter, but if it was my choice, I'd order the thicker ones online.

The same thing happens in other places, e.g. high efficiency toilets have a larger flapper than what is typically stocked in stores, which will make getting replacement parts a pain.

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Amazon is a great resource for this. There was one supplier that made and supplied some very ODD size filters including some with tremendous thickness. – BrownRedHawk Mar 18 '15 at 18:11

I recently went to change the filter in my new furnace and saw that the installed one said it was 16" x 25" x 5". I also couldn't find this size at my local bigbox stores. So I bought a 4" instead. The thing is, it fit perfectly. As it turns out, when I looked at the fine print on the old and new filters, their actual thickness was 4 3/8" in both cases. One manufacturer rounded up to 5, the other down to 4. I just wanted to add this in case others weren't aware of this bit of oddness from the filter makers.

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Huh, my Home Depot and Lowe's both carry the 3m Filters for Media Air Cleaners.

You can order them off of Amazon.

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My Lowe's has 16x25x4" Filtrete media filters (for my own HVAC system) by the bucketload, but last time I was looking for a filter I didn't see a 5". It may be a seasonal thing; usually the best time to do any HVAC maintenance is when your outside temps match your desired inside temp, so most HI stores stock up on those filters in the spring and fall, especially down here in Texas.

If you don't want to special-order a filter, you can probably make due with a 4" disposable media filter, and a 1" reusable plastic mesh filter on top of that (downwind of the media filter to let the disposable one catch the majority of the dust). You shouldn't lose much filter area or efficiency this way.

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