What is the Standard Size of an Air Filter?

Learn how to identify standard-sized and custom-sized air filters for your HVAC unit or central air return grille with this guide.

What is the Standard Size of an Air Filter?

When it comes to air filters, each unit has its own specific size that allows it to operate correctly and efficiently. Most air conditioning and HVAC units use standard-sized filters, but some require the purchase and installation of a custom-sized air filter. To identify the AC filter size, the easiest way is to remove the existing filter from its slot and examine the filter frame. Usually, the size is printed along the edge of the filter frame.

Note that the size shown in bold type on the filter frame is the nominal size of the filter, which is likely to differ from its actual size. If the actual dimensions do not appear in small print on the filter frame, it is recommended to measure the filter for double checking. In this case, you should round down to the nearest integer to determine the nominal size of the air cleaner. The HVAC unit slots are usually located near the bottom of the air handler. 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.

If you have to jam the air filter to install it, you should try a different brand of oven filter or a custom-sized air filter with a slightly smaller actual size. Central air return grilles are usually located on the ceiling of the hallway or on the wall of the hallway of your home. If the return grille is in the ceiling, you may prefer to use a filter that has a slightly larger actual size, so that it does not fall on you when you open the vent. When purchasing a custom-sized air filter, it's important to remember the difference between nominal and actual sizes. Once you determine the exact dimensions that work best for you, place an order for your filter size with exact fraction or decimal of your preferred measurements.

Otherwise, you may get a different actual size than expected. Aerosol ions are effective in reducing bacteria, viruses, odors and other contaminants that exist in your home's air. Placing the filter backwards may cause it to collapse, which will cause airflow to circulate around it. To convert actual size to nominal size, measure your filter and round each dimension to nearest inch. Scroll down to furnace and AC filter sizes in table below and instantly improve air quality by choosing right MERV rating because your family deserves best. For example, Home Depot mainly sells Honeywell brand air filters, while ACE Hardware mainly carries Filtrete.

Watch video for guidance on using oven filter size chart below and hear expert advice to make right choice and avoid common mistakes. If you can't find your size in store or need custom-made air filter, online sellers are probably best option for you. From actual sizes, round measurements to nearest whole numbers when ordering new air filters. If filter fits snugly, use numbers on sides to choose replacement every 60 days or as recommended by manufacturer. The primary function of air filters is to protect your HVAC equipment from damage that can be caused by dust and dirt accumulating on coils.

The goal is for filter to slide comfortably into frame with little wiggle room but not too much. If there is no size on current AC filter, you can measure length, width, depth of filter and corresponding oven filter size in oven filter size table (nominal size).

Amanda Boose
Amanda Boose

Freelance coffee advocate. Evil social media advocate. Hardcore internet trailblazer. Avid twitteraholic. Passionate tv aficionado.

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