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Below you’ll find answers to your most common air filtration questions. Plus, a list of terms and abbreviations commonly used throughout the air filtration industry.

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Air filters can be found inside the heating/cooling system or inside the return grills in your home. These return grills might be on the ceiling or on a wall.

IAQ stands for Indoor Air Quality. This refers to the air quality within and around buildings and structures, especially as it relates to the health and comfort of building occupants. *

Source: https://www.epa.gov

Away from your body, inward toward your HVAC unit. 

Once you find the ‘air flow’ arrow on your new air filter, install the filter ensuring the arrow ALWAYS faces toward the furnace and away from the return duct that carries the air that needs to be heated or cooled into the unit.

How well an air filter removes microscopic particles – such as dust, dust mites, pollen, mold, bacteria, and smoke. * 

Source: https://www.engineeringtoolbox.com

Every 30-90 days. 

Disposable Panel filters, including our Select Series filters, should be changed every 30 days depending on your environment. Disposable Pleated filters, including our Prime Series filters, should be changed every 90 days depending on your environment. High-traffic areas, pets or smoke in your environment, fireplaces, etc. will require more frequent change-outs to ensure the highest air quality possible.

If there is an existing air filter in your return, the size can be found on the frame of that filter. Look for the measurements in this order: Length (L) x Width (W) x Depth (D).

If your return is empty, you can figure out what size air filter you need by measuring the opening of your HVAC return. First measure length and width, then measure depth. Put your measurements together and they read as LxWxD. Reference this measurement when placing your order for air filters and our customer service team will help ensure you get the right size filters for your unit(s).

Actual size is a filter’s true dimensions. For example: 19.5” x 19.5” x 1.5”. Nominal size indicates that the actual measurements have been rounded and is most often used by manufacturers. For example, the nominal size of our actual filter mentioned above would be 20” x 20” x 2”.

You should remove any plastic or wrapping from the filter – but do not remove its cardboard frame. Find your airflow arrow and make sure it points toward the AC/heating blower. Insert your filter into its slot. If your filter is pleated, make sure your pleats are running vertically where possible.

No. The media in our pleated filters, including the Prime Series, is not waterproof. If the media and/or filter becomes wet, the frame may warp, and the media may sag. There is also a potential for mold growth due to build-up in the filter. If you discover your air filter is damp or wet, you should change it immediately.



Mircometer or micron, one-millionth of a meter.


Air Conditioning


Actural Cubic Feet per Minute. This is a measure of air flow referenced to the current density of the gas. The mass flow rate of the air equals the ACFM multiplied by the air density.

Actual Size

The actual size of a filter refers to its exact measurements. It is the filter's true dimensions when you measure the length, width, and depth (thickness). Actual size typically includes a fraction number within the dimensions – for example: 11 1/2" x 19 1/2" x 3/4".


Solid and liquid airborne particles, typically ranging in size from 0.001 to 100 µm.


Ability of a filter to capture a mass fraction of coarse test dust.


ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) is an organization devoted to the advancement of indoor-environment-control technology in the heating, ventilation and air conditioning (HVAC) industry.


A suspension of paarticles of biological origin.


Cubic feet per minute. This is a general measure of volumetric ~ ow rate. Fans are normally rated in terms of CFM. For fan ratings to have meaning, they must be tested under identical, rigidly controlled conditions.

Dust Holding Capacity (DHC)

Measurement of the total amount of dust a filter is able to hold during a dust-loading test.


Measures the ability of an air filter to remove particles from the air stream.

Electrostatic Filter

A filter that uses electrostatically enhanced fibers to attract and retain particles.


Energy has units of force multiplied by distance. It is commonly referred to as "work". the strength and vitality required for sustained physical or mental activity.


Feet per minute; a measurement of air velocity used in calculating cfm requirements.


Grilles are found in residential ceilings and walls but may be installed in floors in certain circumstances. A home can have one larger return grille or several smaller ones throughout the home. The grille’s main purpose is to pull air back into the central heating and air system for reuse.

High Efficiency Filter

Primarily used to collect particles <1 micrometer


Heating, Ventilation, and Air Conditioning


Indoor Air Quality

Low Efficiency Filter

Primarily used to collect particles >1 micrometer


Minimum Efficiency Reporting Value was developed by the American Society of Heating, Refrigeration and Air Conditioner Engineers - ASHRAE.


National Air Filtration Association

Nominal Size

The nominal size of a filter refers to its printed, labeled or rounded size for identification purposes. This size is displayed on the air filter along with the filter’s actual size. It is usually a rounded size, for example 16x20x1.


Original Equipment Manufacturer


Particulate Matter – also known as atmospheric aerosol particles, atmospheric particulate matter, particulate matter, or suspended particulate matter – are microscopic particles of solid or liquid matter suspended in the air.

Pressure Drop

The difference in static pressure measured at two locations in a ventalation system. A measure of air flow resistance through a filter.


Refers to the static-pressure drop across the filter at a given face velocity.


Return vents are connected to your return ducts, which pull air out of your indoor spaces to deliver to your heating and cooling system. They are typically larger in size. Return vents don't have louvers.


Research and Development


Underwriters Laboratories, www.ul.com


Water Gauge