Furnace Filter Question

Old 12-04-09, 09:13 AM
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Furnace Filter Question

I have a relatively new forced air furnace for which I just purchased new filters (2 of them) online because I can't get the right size locally.

Unfortunately, I bought the wrong size. Instead of buying 16x26x5 I bought 16x25x5.

Can I still use the filters? The length is the only place where they're short, and it's only by an inch, but I don't know how much that matters. Is it a big deal? I'd prefer to use them because they're kind of expensive, but the furnace is more expensive, so I don't want to take unnecessary risks.

Old 12-04-09, 11:23 AM
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I'd cut a piece of cardboard to fit the additional length needed and then staple it to the filter.

Basically, you want to plug up the extra length that isn't covered by the filter so a lot of air gets into the furnace unfiltered.

Quite possibly you could do something similar too allow you to use a standard sized filter as a matter of routine. I might be inclined to cut a piece of sheet metal to fit the space the filter should occupy in the furnace, then a slightly smaller hole in the swheet metal that would allow you to use the slightly smaller standard size filter.

A piece of cardboard might work for that, although the force of the air might cause it to collapse over time.

Usually filter sizes aren't real critical to the furnace operation --- a slightly smaller size will probably do fine. The risk is that a smaller filter will restrict the air flow through the furnace enough to prevent the heat produced from being stripped away by the air flow, causing the furnace to over heat and the burners to shut off on the limit switch.

But SLIGHTLY smaller filters PROBABLY wont cause that to happen.

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