How to Change an AC Air Filter

Lawrence Bonk Profile image

Written by:

Updated February 11, 2023

If you are looking to get cool and stay cool during the summer months, you may wonder how to install an air filter in an air conditioner. You may also want to know how to clean air conditioner filters and make your air conditioner more efficient. The best air conditioners, after all, integrate with powerful air filters that filter out impurities derived from the outside air. So how do you get this done quickly and efficiently? Keep reading to find out.


  • Installing an AC filter inside of a window-based AC or a central unit is a relatively fuss-free process and improves indoor air quality.
  • Start by purchasing the correct filter replacement for your specific system. Check the instructions if needed.
  • For window units, you may have to cut the filter down to size using a high-grade pair of scissors.

How to Put in an Air Filter in an AC Unit

This process varies according to the design of your air conditioning unit, particularly if you have a window-based unit or if you’ve learned how to install a central AC unit. If you have a through-wall unit, well, that’s a little tougher. You need to install a slide-out chassis for that A/C. Still, we’ve kept these tips as universal as possible to suit both scenarios.

Insider Tip

Replace or clean filters every one month to three months for best results.

STEP 1 Get the Right Filter

Getting the right filter is paramount to your success in completing this project. If you have a tower fan, you probably don’t have a filter, but you can clean the grille like what we talk about in this Forty4 Small Oscillating Tower Fan review.

  1. Shop around to ensure you purchase the right replacement air filter.
  2. If you have a central unit, check the instructions for information as to which filter to purchase.
  3. Additionally, the advertising associated with the replacement filter could list what systems it works with.
  4. For window units, most general filters will work, though you may have to cut them down to size. This is helpful if you are learning how to install an AC unit in a mobile home.

STEP 2 Cut it Down to Size

For some systems, you’ll have to cut the filter before installing it.

  1. When it comes to central AC filters, you’ll typically not have to cut them down to size, as you’ll have purchased the exact model for your HVAC unit.
  2. For window units, however, you’ll often have to cut the filter to allow it to fit inside of the air conditioner.
  3. Measure the filter opening and use a high-quality pair of scissors to cut the filter to the appropriate dimensions.

STEP 3 Insert the Filter

Now it’s time to put in the new filter and enjoy the cool and fresh air.

  1. For window units, simply open up the door containing the old filter, remove it, and slide in the new one. There should be hooks that catch the filter to hold it in place.
  2. For central units and HVAC systems, find a door marked “filter” somewhere near or inside of the air handler cabinet.
  3. Remove the old filter and replace it with the new one.


Need help with HVAC maintenance?

HVAC maintenance is a complicated topic, as HVAC systems include many parts, such as return ducts, clean filters, a furnace filter, and more. Contact service technicians for specific information and jot down their answers with a permanent marker.

What’s the best type of filter to use?

This depends on your individual AC unit. Purchase and install the replaceable filter or reusable filter that works with your system.

How bad is it if I don’t change my filter?

It’s bad. Allowing a dirty air filter to fester contaminates the air and could lead to mold growth and increased energy bills.

STAT: How often to change filters will vary based on the type of filter you have. For example, a basic, 1-inch air filter will most likely need to be replaced more often than a larger 4-inch filter. (source)

Lawrence Bonk Profile image