Updated: January 2024

When it comes time for St. Louis area homeowners to change the filter in their furnaces, there are many things to think about.

If you’re happy with the performance of your current filter, you can simply replace it with the same brand and model that you’re currently using. If you’re not satisfied with it, you’ll want to look into filters that are made of different materials or possibly invest in an air cleaner.

But one thing you’ll always need to know when you’re changing any kind of filter is what furnace filter sizes are right for your unit. So how do you know what those are?

How to determine the right furnace filter sizes for your unit

The easiest way to find out what size filter to get for your furnace is to simply remove your current filter and look at its dimensions. These are typically printed along with one of the sides of your filter.

One thing you’ll want to be aware of is that the actual size of your filter will vary slightly from what’s printed on it – sometimes by as much as a half an inch smaller for each dimension. For example, your filter might read 16″x20″x1″, but if you measured with a ruler, it might be something like 151/2“x193/4“x3/4”.

The reason for that is air filters need to be slightly smaller than the slots that they fit into so that they can be easily replaced. If your filter was the same size as that slot that it fits in, it would be very difficult to install and remove it.

What if you can’t find your current furnace filter sizes?

If for some reason you can’t find the dimensions printed on your current air filter, don’t fret. All you’ll have to do is measure the height, length, and width of your filter and round up to the nearest whole number.

If you’d like any help choosing the right sized filter for your furnace, contact Jerry Kelly Heating & Air Conditioning, your St. Louis area heating and cooling company

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