When it comes to air filters, there are a variety of sizes available. The most common sizes are 20 x 20 x 1, 16 x 25 x 1, 20 x 25 x 1, 20 x 25 x 4, 16 x 20 x 1, 16 x 25 x 4, 20 x 30 x 1, and 12 x 12 x 1. It's important to note that these sizes are nominal, meaning that the actual measurements may be slightly different. For example, a 20x20x1 air filter is actually 19-¾ x 19-¾ x ¾.
This is known as undermining and is done to provide a little headroom and ensure the filter fits in the air return without being too large. It's also important to note that the orientation of the filter doesn't affect its effectiveness. This means that a 20x30 filter and a 30x20 filter are essentially the same size. This reduces the number of unique air filter sizes on the market by half. It's best to have a little wiggle room in the slot of the HVAC unit, so you can easily slide the filter in and out without it bending or breaking. When buying air filters online, it's important to make sure you get the right size.
If the filter is too small, it won't fit in the slot and air flow could be restricted. If it's too large, the frame will wrinkle, air flow could be restricted, and longevity would be compromised. The length, width, and depth of a filter are printed in small quantities along the filter frame on the cardboard edge of a Filter King brand filter. If you have 1 or 2 air filters that aren't on this list, you may need a custom cut. The easiest way to identify the size of an AC filter is to remove the existing filter from its slot and examine the filter frame.
You can also find the proper air filter dimensions listed in your HVAC manual. In this case, you'll need to round down to the nearest whole number to determine the nominal size of the air filter. Whole house filters usually go to an air controller, which is usually located next to the HVAC system itself. There are several great options for buying air filters online and having them conveniently delivered to your door.