Two plus two may equal four in most situations, but not when it comes to air conditioner filters. Why? The measurements listed by filter manufacturers may or may not be the actual size of the filter.

And air filter size is extremely important for air quality. The wrong filter will leave you breathing in the dust, irritating allergens, and other things you were hoping to avoid.

So, how can you choose the right air conditioner filter sizes?

Read on as we share with you a few tips on how to navigate the sometimes confusing world of air filters. Afterward, you’ll be able to correctly match filters with your air conditioner.

Standard Sizes Aren’t Standardized

It would seem logical that if two manufacturers produced filters both labeled as 25 inches wide, the filters would be the same width. But that’s not the case.  

Try conducting an experiment. The next time you’re in the hardware store, place rival filters side by side. The difference will be small but significant.

Why are they different lengths? There is no industry oversight committee mandating that the filters must perfectly match their descriptions. We mentioned width in our example, but the discrepancy could also be in the length and thickness of the filter. 

The result is that one or neither of the filters may be an ideal match for your air conditioner. So, you’re going to have to do some homework.

Determining Your Air Conditioner Filter’s True Size

Air conditioner filter sizes are typically listed in the order of width, length, and thickness. A filter listed as 20x25x1 is 20 inches long, 25 inches wide, and 1 inch thick.

If you measure the filter, you’ll find that it comes up short of those measurements. But it’s marketed as 20x25x1. 

The problem is the dimensions of the slot where your air conditioner houses its filter probably won’t match the filter ideally. If the filter is too small, unfiltered air can get into your system and eventually into your indoor air.

If the filter is too large, you’ll have to squeeze it into its slot. If it buckles, it too will allow unfiltered air into your space.

Measure your air conditioner’s filter slot. Be sure to get the interior dimensions. Then measure the available filters at your hardware store. Choose the closest match to your air conditioner’s measurements.

Why Worry About Filter Size?

Most homeowners overlook the importance of a good filter. After all, it costs only a fraction of what the HVAC costs. 

But minimizing the role of the filter can lead to getting less out of your air conditioner. A poorly-fitting filter can allow so much unfiltered air into your system that it’s the equivalent of operating your air conditioner for part of the day without a filter. 

In time, debris in your system can cause it to work harder than it should. In turn, your HVAC can need maintenance far more frequently than normal.

You and your family will also notice the effects on indoor air quality. A filter should prevent allergies and reduce dust in your environment.

But the wrong filter opens the door to airborne particles, helping them freely circulate in your home. This is especially dangerous for anyone with dust mite allergies or respiratory issues.

Get Expert Advice About Air Conditioner Filter Sizes

If you need additional advice about air conditioner filter sizes, our skilled technicians would love to hear from you. We have familiarity with a wide variety of manufacturers. We can use our experience to guide you toward the filter that’s right for your system.

Contact Sewell Electric & HVAC today to make sure your air conditioner has the right filter.