What are the best types of air conditioning filters?

Types of Air Conditioning Filters

Air conditioning filters purify the air from pollutants, odors, dust, and bacteria. The materials used in filters, their functions, and the degree of purification vary depending on where your air conditioner is located and what kind of air quality you want to achieve. For example, in residential buildings, filters purify the air from dust and odors inside the building. In central air conditioning systems, they also purify the air coming through the air ducts. Hospitals, laboratories, and some industries, however, require higher purification rates to remove germs, viruses and toxic gases from the air.

1-Classification by air conditioning system

1. Internal Air Conditioning Filters for Window or Split Units

These are plastic mesh filters that purify the indoor air of the room from dust particles in the air. Internal filters for central a/c, usually located behind the air intake opening, operate similarly to filters in ordinary a/c and perform the same function. These filters are cleanable on a regular basis. High-efficiency filters (central a/c) such as HEPA filters purify the air coming out of rooms to prevent infection in hospitals. These filters need regular replacement and proper disposal.

2. Filters in Central Air Conditioning Units with Air Handling Units

In addition to the (cooling/heating) process, these units also include humidification or dehumidification processes. They have a filtration section that purifies the air from dust using filters with varying degrees of precision. These filters may include filters for purifying germs and viruses with very high efficiency.

There are different criteria to select filters: the function of the space, the required air quality, and filtration efficiency.

2-Classification by air conditioning filters efficiency

ASHRAE Standard 52.2 provide classification of filter efficiency according to the amount of particle size trapped by the filter. Accordingly, the minimum filtration efficiency (Minimum Efficiency Reporting Value) MERV is determined, starting from 1 MERV to 16 MERV.

-The international test standard ISO 16890 includes the degree of filtration based on the practical mass in three different size fractions PM1 (0.3-1 µm), PM2.5(0.3-2.5 µm) and PM10 (0.3-10 µm).

3-Classification by air conditioning filters shapes and materials

These filters come in various shapes, sizes, and different materials depending on their installation location and the desired filtration level. They include the following:

  • Regularly Cleanable Filters: These filters are designed to be cleaned regularly to remove dust and dirt particles that accumulate on them. Accordingly, they include plastic mesh filters found in split and window air conditioners, aluminum frame mesh filters used in central air conditioning systems indoors or outdoors, and they can have different opening sizes depending on the filtration accuracy. These filters are primary filters, installed before other filters to capture large particles in the air and prevent clogging. The main function of these filters is to absorb unpleasant odors.
  • Carbon Filters: The primary function of these filters is to absorb unpleasant odors.
  • Fiberglass Filters: These filters are made of stacked bags and considered the least effective.
  • Polyester Filters: These filters consist of zigzag layers placed within a frame and have high airflow resistance.
  • High-Efficiency Filters (HEPA): These filters are useful in hospitals and places that require high efficiency in trapping bacteria and germs. Therefore, they must be replaced periodically and disposed of with special care.

The airflow resistance

When selecting filters, it is important to consider the airflow resistance caused by the filters within the air ducts in the air conditioning system to ensure that the fans have the necessary power to overcome this resistance. The airflow resistance is specified in the charts provided by the manufacturers.


The filtering of the air inside building is one of the main jobs of air conditioning system. Therefore, it is important to choose the appropriate filters for your system, that you can ensure the air in your home or business is clean, healthy, and comfortable. Finally, if we want to take care for our air conditioning system, we should clean it regularly or change the filters if needed.

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