Air filters come in a variety of sizes, and it's important to know the difference between the actual size and the nominal size. The actual size is the exact dimensions without rounding, while the nominal size is the rounded dimensions of the filter. Most air conditioning and HVAC units use standard size filters, but some require a custom-sized air filter to be purchased and installed. When buying an air filter, it's important to keep in mind that the industry standard for air filtration is to have the filters measure slightly smaller than their slot or frame, so that they can easily slide into place without bending or breaking.
To determine the correct size of an air filter, measure the length and width (L x W) of the inner edge of the slot or frame of the air cleaner. Then, round down to the nearest whole number to determine the nominal size of the air filter. Most large retailers, such as Walmart, Target and Home Depot, have air filters available for purchase. However, if you can't find the size you need at a local store, HVAC service companies often offer air filter replacement services in addition to system repair and unit installation services.
It's essential to use an appropriately sized air filter for your HVAC unit to keep the system running smoothly and take advantage of all the benefits that the air filter offers. Installing several 1-inch air filters in a 2-slot, for example, can cause costly damage to the air conditioning unit, since residential ovens are not equipped to withstand this level of air flow restriction. Colorfil filters, originally created for NASA, help remove chemicals and odors at a molecular level that normal air filters can't remove.