Why are There so Many Air Filter Sizes?

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Heather Jones
Heather Jones
I'm Heather, an author passionate about home improvements. My writing is your guide to making homes better. Let's explore easy ways to enhance your living spaces, from small fixes to exciting projects. Join me on a journey of making your house a cozy and stylish haven.

If you are replacing your home air filter, you need to choose the right size. But there are many options. In addition to having multiple standard sized filters, most companies also have a variety of custom sizes. Learn why there are so many air filter sizes, and find out how you can figure out the size of your filter. Then, you can keep pollutants out of your home.


Why is There So Much Variation?

There is no single standard size of air filter. Rather, there are over ten standard filter sizes. And there’s a reason for this. The size of your filter depends on the size and layout of your HVAC system.

Every HVAC system is unique. Even if systems are created by the same company or installer, they differ. They have different layouts. You can’t be sure where your filter is until you see it for yourself.

For this reason, there are multiple filter sizes. If you’ve never replaced your filter, you need to be certain to find the right size before buying a replacement.

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Does the Filter Size Actually Matter?

The size of your filter does matter. This is because your filter needs to fit perfectly in the housing. If the filter is too big, it won’t fit at all. If it’s too small, it won’t get the job done. Small and large particles will get sucked up by your HVAC system. Then, those particles go back into your home and impact your air quality.

Fortunately, finding the proper size isn’t as difficult as you might imagine. And once you know the size, you can record it so you remember it the next time you need to order a filter.

Tips for Finding the Right Size

 Determining the size of your filter is simple. Follow these steps and you can figure out what size you need to order.

1. Take Out Your Old Filter

By removing your old filter, you can find out how big your filter needs to be. However, you first need to be certain the old filter was the right size. Look for gaps between the filter and the housing. Additionally, you should determine whether or not the old filter was crammed into the housing. If the fit is too tight or too loose, you may need to size up or down.

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Your filter might say the dimensions on it. However, those dimensions could be faded. Inspect your filter for dimensions. If it fit well in the filter housing, then you should order that dimension. But if there are no dimensions, you might need to go to the next step to determine the size.

 2. Measure the Filter

Pull out your measuring tape and measure the dimensions of your old filter. Filters have three sizes – the length, width, and depth. For example, your filter might be 18x20x1.

Filters are often sold in nominal dimensions. Typically, filters aren’t cut to exact size. In fact, they may be ⅛” or ¼” smaller than the actual dimensions. This ensures that your filter will fit your space. When the HVAC system is on, it will seal the filter to the housing. When that happens, the small difference in size is irrelevant.

3. Consult Your HVAC Manual

You can also check your HVAC manual for information on your filter size. In the manual, you can find the exact dimensions of your air filter.

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