Do all air filters fit the same?

Standard air filter sizes may vary slightly; air filters are not designed to be adjusted. In fact, if you have to force an air filter in or out, it's the wrong size, so standard sizes are usually half an inch smaller than advertised. No, HVAC air filters differ in quality and dimensions, and some have features that others don't. In most cases, we recommend using the filter that your HVAC manufacturer recommends matching with your system.

We can manufacture air filters in any custom size you need. These are not imperfect filters, pre-made and cut to size. They are built from the ground up using their exact dimensions. All filters have two different sizes.

All filters have an actual size and then a nominal size. The actual size is the exact dimensions without rounding; while the nominal size is the rounded dimensions of the filter. This means that for air filters 1 and 2, the nominal size does not include the notch, and the actual size does include the recess. For whole-house filters, the nominal size is the rounded size and the actual size is only the unrounded one.

Whether you're measuring wood or air filters, it's important to note that the nominal size is not the same as the actual size. But what does the nominal size mean anyway? Know the difference between the two dimensions and buy your air filter with confidence. When making your purchase, you should order the filter by its nominal size, rather than its actual size. Note that the size shown in bold type on the filter frame is the nominal size of the filter, which is likely to differ from its actual size.

Filters don't need to fit a “tight seal”, but you should be able to easily install and uninstall the filter effortlessly. While you may be tempted to use a HEPA filter, know that it's like putting a MERV 16 filter in your HVAC unit. For common brands of HVAC systems such as Goodman, Lennox, Trane, Rheem York, Coleman and Carrier, most standard air filter sizes will work. In fact, most residential HVAC systems are specifically designed to work with a filter with a MERV rating of less than 13.If the filter pleats extend horizontally or vertically, it won't affect the effectiveness of your filter, so the number of unique air filter sizes on the market can be halved.

Always list the smallest measurement first instead of having a 20x30 and a 30x20 as two completely different products. In this case, you'll want to round down to the nearest integer to determine the nominal size of the air cleaner. Most white pleated air filters are inherently the same within each efficiency level, and vary slightly, if at all, between brands. Each brand makes filters with slightly different actual sizes, so check the exact measurements of each filter before purchasing.

If you're looking for a retailer near you that sells custom-sized air filters, you might struggle to get lucky. You can find the recommended filter size for your unit model here in the table titled “Find your air conditioner and oven filter by make, model number and size. If you have a 1 or 2 air filter that isn't on this list, chances are you'll need a custom cut, and the hardware store definitely can't help you here. Here's a fun fact: 70% of what Filterbuy sells falls outside the 10 most common air filter sizes.

Janice Kampman
Janice Kampman

Subtly charming musicaholic. Zombie evangelist. Incurable travel lover. Devoted beer enthusiast. Passionate zombie specialist.

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