Understanding Actual Size vs. Nominal Size in Air Filters: What’s the Difference?

Ever ordered an air filter, only to get it and think, “Wait, this doesn’t look like the size I ordered?” You’re not alone! In the world of air filters, there’s a bit of a language quirk that trips up many people: the difference between nominal size and actual size. But don’t worry, once you know the basics, you’ll be a pro at ordering the right size filter every time!

What is the Nominal Size?

Think of the nominal size as the “nickname” of the air filter. It’s a rounded measurement that makes life easier for manufacturers and sellers (and sometimes confusing for us!). You’ll see these on filter packaging, and they typically come in whole numbers, like 16x25x1 or 20x20x1 inches. While it’s close to the actual size, it’s not exactly precise.

So why even use nominal sizes? Good question! Nominal sizes give us a standard way to refer to filters without bogging us down with exact details. It’s kind of like saying, “I’m a size 10 in shoes,” even though some brands might fit a bit differently.

What is the Actual Size?

The actual size is the real deal. It’s the precise, down-to-the-millimeter measurement of the air filter itself. If you took a tape measure to your filter, you’d see measurements like 15.5 x 24.5 x 0.75 inches for what’s labeled as a “16x25x1.” These actual sizes are smaller than the nominal size on purpose to make sure your filter fits snugly in its slot.

This slight difference accounts for the space needed for the filter to slide in and out smoothly. Actual size measurements are usually shown on the side of the filter in smaller print. For example, if you ordered a 16x25x1 filter, the actual size might read something like 15.5 x 24.5 x 0.75 inches.

Why Does It Matter?

Knowing the difference between nominal and actual sizes matters because your filter needs to fit properly in your HVAC system to do its job. A loose filter can let dust, allergens, and other particles slip by, which defeats the purpose of having a filter in the first place! And a filter that’s too tight could end up bending or damaging your system.

Here’s the quick rule of thumb: Always check the actual size on your filter before you buy a new one. This way, you’ll know exactly what dimensions your system needs.

Quick Tips for Choosing the Right Size

• Use the actual size as your reference. If you already have a filter, take a peek at its side where the actual size is printed. Keep those measurements in mind for future orders.
• Go custom if needed. If your system requires a unique fit, some companies (like us!) offer custom filters for non-standard sizes, so you get the perfect fit every time.

In Short...

Nominal size is the convenient label; actual size is the true measurement. With this simple guide, you can avoid those pesky sizing surprises and keep your HVAC system working like a charm. For even more in-depth tips and insights, check out our blog here! We’re always here to help you find the perfect fit!