If you know the actual size of your air conditioner filter, it's easy to determine the nominal size. All you need to do is round each dimension to the nearest inch. The filters are labeled with three-part dimensions, with the first number being its length, the second being its width, and the third being its depth or thickness. To find the size of your AC filter, you can look at the size chart which lists standard sizes for 1 inch, 2 inch, and 4 inch deep air conditioner filters.
This is the easiest way to find out the size of your filter, but not all filters have size measurements listed on them. Additionally, suppliers may be incentivized to increase the sale of certain types or brands of air filters. HVAC service companies typically offer air filter replacement services, as well as system repair and unit installation services. To the right of the filter, it also includes the actual filter size, which are the true measurements of the filter dimensions by length, width, and depth.
It should fit snugly into the air cleaner compartment with a little space around the edges. Standard sizes for air filters are approximately 20” and none have the same measurements. 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. Lennox has a MERV 16 filter option as an offer on their Lennox Pureair system, which is among the highest-efficiency residential filters available and Lennox also recommends it as an upgrade to specific Carrier, Trion Air Bear and Honeywell systems.
If the filter is too small, it will loosen and some of the air (and dirt) will not pass through the air filter. There are hundreds of varying sizes of oven filters because they are all different sizes. Each mark may have actual sizes that are different from the nominal size (the size on the label is sometimes a rounded size) that appears on the filter label. Installing several 1-in-a-slot air filters can cause costly damage to your air conditioning unit, as residential ovens are not equipped to handle this level of airflow restriction.