When it comes to air filters, understanding the most common size can be a bit of a challenge if you're not sure what the numbers mean. The nominal size is usually printed on the cardboard edge of the air filter and is the only one you really need to know when looking for one. It's important to note that the nominal size is not the same as the actual size. To determine the actual measurements of an air filter, simply measure each side of the filter with a measuring tape.
In most cases, you should be able to use the closest standard size. However, if there is any resistance to airflow caused by using a filter that is not the correct size, it can cause unnecessary stress on the HVAC unit itself, which could damage the system equipment and increase your energy bills. Do not stack several smaller air filters on top of each other to place them in a larger air handling unit. Installing several air cleaners 1 in a slot of 2, for example, can cause costly damage to the air conditioning unit, since residential furnaces are not equipped to withstand this level of airflow restriction.
Money may not be the only thing you'll save by changing air filters regularly, as it helps prevent premature furnace failure. If an air filter is too small, air gaps will be created and contaminants will bypass the filter material. When you buy air filters, you will see the words “nominal size” and “actual size” together. The number is then usually rounded up and used to label air filter packs; this measurement is known as the nominal size.
There are a number of great options to buy air filters online and have them delivered to your doorstep comfortably. If you're looking for a retailer near you that sells custom-sized air filters, you might be struggling to get lucky.
