Buying Odd-Sized, Non-Standard Furnace Filters?

Weird topic, but shortly after we moved into our house, I noticed that we have two apparently non-standard air returns. The openings measure 5.5 x 13.5 inches, and so we need filters that are 5.375 x 13.375 inches. Unfortunately, I haven’t been able to find anything to fit these dimensions.

We’ve always used the cheap spun glass filters and swapped them out every 30 days or so. Since the move, I’ve been doing the same thing for the standard air returns, but for the odd-shaped returns I’ve been pulling the filters out monthly, vacuuming them, and sticking them back in. While that’s been a workable short term solution, I’d like to actually solve this problem.

From what I can tell, the previous owners had custom filters made, and I’ve found a couple of places online that offer to do this for you. The problem is that it’s fairly costly… While you can get standard filters for $2 apiece, the prices for custom cut filters start around $6 each. On the other hand, cutting the filters down and then re-attaching the cardboard ‘frame’ isn’t as easy as it looks, so… I was wondering if anyone has any suggestions? Either a cheaper source for 5.375 x 13.375 inch filters, or perhaps another solution entirely?

6 Responses to “Buying Odd-Sized, Non-Standard Furnace Filters?”

  1. Anonymous

    You can get a custom made washable, reusable furnace filter made. The upfront cost might be a bit high, but in the long run, since you can use it over and over and over, it’ll be worth it…espescially since you have a wacky size.

  2. Anonymous

    Without seeing it first hand, it’s tough to know what will work, but I’ll assume your furnace filter housing looks a little like mine, and suggest from there.

    How about cutting a foamcore, cardboard, or matte board (depening on how wide the filter slot is) rectangle to the exact dimensions you need, then purchasing the filter that is closest without going over (to quote Bob Barker)? Just cut out the center of the rectangle to match the smaller filter, and the frame will seal the gap. Should be reusable many times. Might need a little duct tape to hole the filter in place to the frame. The blower has a pretty good draw on a forced air furnace, and will suck the frame to the housing, providing a good seal even if it is slack when the furnace is not on.

    I purchase filters from, and have been pleased. We have a big replace-once-a-year filter, which can be pricey.

  3. Anonymous

    Hmmm, that is a weird size.

    The cheap-a$$ that I am I’de probably investigate making my own reusable frame from wood and chicken wire. You can probably buy one of the larger $2 20×20 filters and cut 3 refills out of it for a home grown filter.

    — Dave

  4. Anonymous

    How much would it cost and how difficult would it be to replace the air returns with a standard size or else build some sort of adapter so that you can use a standard filter?

    If that is out of the question, I’d just shop around to see if you can find a way to get the custom sizes for the cheapest price and then just use the one filter w/a vacuum until you’ve gotten the money’s worth compared to standard sized and replace at that point.

Leave a Reply