In most cases, you can use the closest standard size for your air filter. To find the size of pleated filters used in your home, look no further than your existing filters. In the outer frame, you'll see at least one set of numbers. If you see two sets of numbers, the filter size needed to request replacements is the nominal size, not the actual size.
You can ignore the actual size printed on the filter for this task. Do not stack several smaller air filters on top of each other to place them in a larger air handler. A higher MERV rating means that an air filter is more effective at removing the smallest particles from the air. There are thousands of sizes of air filters, and HVAC manufacturers make it complicated so that you get stuck paying for their overpriced replacements.
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. For air filters, the dimensions of length and width are interchangeable, although conventionally the largest of the measurements is the width and the shortest is the length. Colorfil filters, originally designed for NASA, help eliminate chemicals and odors at a molecular level that normal air filters can't. With all the available air filter sizes, it can be overwhelming to find the right one for your air conditioning unit.
Please note that the actual size of the air cleaner will be smaller than its nominal size. For many people, air filtration is a confusing topic, where questions are often not asked or answered. Remember that filters should be slightly smaller than their slot to allow easy removal of the old and installation of the new one. When buying an air filter, it's important to keep in mind that industry standard is to make filters measure a little smaller than their slot or frame, so they can easily slide into place without bending or breaking. If an air filter is too small, this will create air gaps and contaminants will avoid filter material.
Since air filters are most often sold for their nominal dimensions, it is essential to learn how to properly measure your air filter.