The filters used in air conditioners are labeled with three-part dimensions. The first number is its length, the second is its width and the third is its depth or thickness. Most pleated and white air filters are similar within each efficiency level and may vary slightly between brands. If an oversized filter is placed in the wrong spot, it can damage the HVAC system and not clean the air properly.
If your current air conditioner filter does not have any size, you can measure the length, width and depth of the filter to find the actual size of your filter with the corresponding oven filter size in the oven filter size chart (nominal size). If you have to force the air filter to install it, try a different oven filter or a custom-sized air filter with a slightly smaller actual size. The most common air and oven filter sizes are the 16x20x1 air filter, the 20x20x1 air filter, the 16x25x1 air filter, and the 20x25x1 air filter. HVAC service companies often offer air filter replacement services in addition to system repair and unit installation services. You can find the recommended filter size for your unit model in the table titled “Find your air conditioner and oven filter by make, model number and size”.
Placing the filter backwards may cause it to collapse and allow air to flow around it. The primary purpose of air filters is to protect your HVAC equipment from damage caused by dust and dirt accumulation on coils. If a filter is not properly adjusted, unfiltered air will pass through the path of least resistance and make the filter partially or completely useless. Lennox offers a MERV 16 filter option in its Lennox Pureair system, which is one of the most efficient residential filters available. Lennox also recommends it as an upgrade for specific Carrier, Trion Air Bear and Honeywell systems.
If you live in an older house with a non-standard size air return structure, you can use adhesive foam weatherstrip tape to slightly increase the dimensions of your favorite filter or order a custom-sized air filter. The actual size of the filter is also included to the right of it, which are its true measurements by length, width and depth. If you're using a room air purifier and need to replace its filter, it's important to find the right size replacement HEPA filter.
