How to Locate and Change Your AC Filter

Where is the Filter for My AC Unit?

The air inside your house will always have dust, pollen, lint and other forms of impurities suspended in it. Apart from cooling it, an air conditioner (or HVAC system) is also designed to filter/clean the air.

That is usually done by a filter which is installed just before the air enters the HVAC system’s furnace or air handler


In a newly constructed house, the AC filter should be replaced after every month. After that or in older houses, AC filters should be replaced quarterly. That means 4 times in a year.

Most folks however do not replace their AC filters as often as they should. The main reason for that is because they do know where the filter is located. So, where is the AC filter located in the house?

The AC unit air filter is located where the return air duct enters the furnace/air handler, or just behind the return air grill on the ceiling or wall. Your furnace or air handler will be located in the basement, attic, and crawlspace or in a utility closet.

If you can locate your water heater, you can also locate your furnace or air handler. The 2 appliances are always installed close to each other.

In horizontal HVAC units, the air filter will be located on the return air ducts, on the left-hand side of the furnace/air handler. With vertical HVAC units, the filter is usually located in a slot at the bottom of the furnace or air handler.

In some air conditioners, the air filter is located just behind the return air vent/grills. You many need to look in each return air grill if you have one in each room. Return air grills are found on ceilings, walls, or utility closets.

Do All Air Conditioners Have an Air Filter

All air conditioners air (central air conditioners and heat pumps) have an air filter. AC filters are always located in the return air ducts or sometimes inside the air handler or furnace just before the return air enters the blower or furnace.

Note: If you have a central air conditioner, it will be paired with a furnace. On the other hand, if you have a heat pump, it will be paired with an air handler. More on that in this post.

Most HVAC systems have one air filter located where the return air duct enters the air handler or furnace. The system could however have several filters if you have multiple return ducts.

To change your AC filter you just need to locate it, remove the small cover and then slide the filter out. To correctly put in the new one, make sure that the arrow indicating air flow direction is pointing towards the furnace/air handler.

Failure to change your AC filter means that it will get clogged by dirt and therefore restrict intake of air. The HVAC system will therefore need to work hard to cool or heat the air in the house which means it will be inefficient. That will also greatly reduce its lifespan.

If you live in an apartment, the AC unit will be located somewhere in a closet. Look for a slot with a removable cover and easily slide out the filter if you need to change. If not, look for it just behind the return air grill on the ceiling, wall or closet.

How to Locate Your AC Unit Filter in the House

There are 2 places to locate an AC filter:

  • Behind the return vent grill
  • In the air handler/furnace

1. Behind the Return Air Grill

Locating an AC filter is often thought of as daunting task but it ought not to be. The surest way of locating the AC filter is by following your air conditioners return air duct.

I think at this point I should explain what a return air duct is in case you are wondering what it is.

An HVAC system has a return air duct and a supply air duct. Both carry air away and to the house and are connected to the air handler or furnace.

When the thermostat calls for heating or cooling, the fan in the air handler or furnace starts turning, thereby pulling air from the house. Air from the house flows to the air handler or furnace through the return air duct.

After cooling or heating the air, the unit sends the cooled or heated air back to the house through the supply air ducts.

Inside your house, you will have the AC return air vents and supply air vents. Those are the grilled openings on the ceiling, wall, or utility closet.


The difference between AC return and supply air vents is that the return vents are larger in size. If you want to be sure, place your palm on the vent when the AC fan is on. If there is a suction effect on your palm then that indeed is the return vent.

To check if the filter is behind the return air grill, remove the grill by pulling the tabs (no tools needed) and have a look. If it is there just remove and replace it.

Note: The filter should fit snugly and should never be forced in such that it bends. Always be sure about the size. Secondly, make sure the airflow arrow is pointing towards the air ducts (away from the house)

2. In the Air Handler/Furnace

There are 2 types of air handler/furnaces depending on how they are installed. These are:

  • Vertical HVAC units
  • Horizontal HVAC units

Vertical HVAC units are usually installed in areas where space is limited while horizontal units are installed in huge basements and attics. That also affects how return and supply air ducts are connected to the unit.

In vertical HVAC units, the return air duct enters the unit at the bottom of the unit while the supply air duct exits the unit from the top compartment.

On the other hand, in horizontal units, the return air duct enters the unit from the left-hand side while the supply air ducts leaves it from the right-hand side.

What you need to know is that the air filter will be located very close to where the return air duct enters the unit, before the air enters the blower compartment. In the case of a horizontal unit, that will be on a small slot on the left-hand side of the unit.


If you have a vertical unit, look for a small slot just where the return air duct is entering the unit. If not there, look for it at the bottom of the unit. Air filters are usually about 1-inch in width so the slot will be almost about the same size, although some air filters are as wide as 4-inches.

How to Change/Replace an AC Air Filter

Changing an AC air filter is the easiest thing. Finding it is harder.  Here are the steps to follow:

  • Start by turning off your unit. Remember that the filter will be full of dust. Attempting to pull it with the fan still running will result in the dust being sucked inside the system, which is what you have been avoiding all that time.
  • Remove the filter cover. The cover is either fully removable or hinged.
  • Slide out the filter. It just pulls out smoothly. While pulling out note the direction in which it was installed. All filters have an arrow. The arrow should always point towards the air handler/furnace.
  • Buy an exact same filter. AC filters have their sizes written on them. Make sure you buy a filter of the same exact size.
  • Slide in the new filter. Again, make sure that the airflow arrow is pointing towards the unit.
  • Put back the cover.
  • Turn on the unit.

Wrap Up

And basically that is how to locate and change the AC filter in your house. I hope that you found this guide to be helpful