Where do air Filters go?

September 5, 2020
Buying Home Air Filters 101

Photograph of central air returnInspectAPedia

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  • AIR FILTER LOCATION - CONTENTS: How to Locate or Find the Air Filters on Heating and Air Conditioning Systems - where to look for air filters if you cannot find them on your system. Central Air Return Registers and Filters on Air Conditioning or Heating Systems
  • about the location of air filters on air conditioning & heating systems

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Where air filters are installed on air conditioning or heating systems:

This article explains in detail how to find the air filters on an air conditioning or hot air heating system.

Knowing where air filters are typically located can help find dirty or clogged air filters that are increasing air conditioning or heating cost. Before assuming that your HVAC system does not have an air filter installed, or that it has only one air filter installed, check the locations we describe here.

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AIR FILTER LOCATION - How to Find the Air Conditioning Filter on Air Conditioners or Hot Air Heating Systems

If you can't find your air conditioner system filters (there may be more than one air filter) here are some places to look. After reviewing this list of air filter locations, if you still cannot find your heating or air conditioning system air filter read our detailed instructions on how to find air filters which follows just after this list.

  • At the central air return register, grille located in a wall or ceiling if your system uses centralized air returns instead of individual room-air return ducts. There may be several central return points, depending on the design of your system. If there are more than two, chances are the filter was placed at the air handler instead of at these grilles. Unfortunately that means that the return ducts themselves become more soiled with dust and debris from the building.
  • At an attic air handler look for a slot which has a removable cover. The slot may be just an inch or so wide if 1" thick filters are used, or it could be several inches wide if a wide high-capacity pleated or similar filter was used. The return air plenum on an attic or basement air conditioner blower unit will usually be a large metal enclosure about the same dimensions in width and height as the air conditioner blower unit itself.Photograph of unsafe basement reuturn air grille Look for a filter slot right where the return plenum contacts the blower fan assembly.
  • At a basement air handler we also look for a filter at the return air plenum which is often next to the bottom of the air handler if the system is an "up-flow" unit (or vice versa for the less common case of return air entering at the top of the air handler and exiting at its bottom).
  • Next to an electrostatic air cleaner: if your air conditioning air handler has an electrostatic air cleaner installed, look for the filter, if there is one, next to the electrostatic air cleaner. In addition, the electrostatic air cleaner, which is a type of particle incinerating filter itself, needs to be removed and cleaned periodically.

    In our photo at left, the silver handle above the white electrostatic air cleaner is a tip-off that a removable filter is installed there.

    Check with your unit's manufacturer for cleaning interval and procedures. Often the electrostatic unit can be cleaned inside a dishwasher. Often there is also a thin metal washable air filter installed along with the electrostatic air cleaner.

A Detailed Guide on How to Find the Air Filters on an Air Conditioning or Heating System

Central air conditioning filters (or heating system filters if hot air heat is used as well) are sometimes hard to find. Here are some tips on where to look to find the filters on your central air conditioning system:

Central Air Return Registers and Filters on Air Conditioning or Heating Systems

Central air returns - Air conditioning filters located on central air return registers: if the system uses one or just a few central return registers very often a filter is placed behind the inlet grille at the central air return and is easily spotted in installations such as this Arizona central air conditioning air return inlet in the ceiling of a new home - the large rectangle is a return inlet where the air filter is quite visible.

In this photo the small opening is a poorly-installed supply register - air coming out of this register will simply be drawn right back into the return air inlet and won't do much good for the rest of the building.

Look for central air returns on building ceilings and walls in central areas such as in the ceiling near the top of a stairwell to an upper floor, or on lower floors look on hallway ceilings. Don't forget to look for central air return registers on floors too, such as shown in this photo of an air return in a front hallway floor.

Sometimes there will be a central air return in a ceiling or wall but without any filter (as shown in this photo of a wall-mounted return air inlet). In that case we'd expect to find an air filter at the air handler unit. It would have been better to put the filter at the wall or ceiling return register grille since that way the return air ducts are protected from debris accumulation.

Photograph of an old supply air register Photograph of an old supply air register Photograph of attic air conditioning Photograph of vertical upflow  air conditioning
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