Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

Air Filters - Arrestance and Efficiency

Air filters efficiency and arrestance.

The mission of an air-filter is to remove particulate or gaseous materials from the air-stream and efficiency and arrestance are used to describe filter functionality.

Air Filter Efficiency

Efficiency describes how well an air filter removes microscopic particles - such as dust, dust mites, pollen, mold, bacteria, and smoke.

In the ASHRAE 52.1 Standard test method, efficiency is a measure of ability to remove the staining portion of atmospheric dust from test air - officially termed "Atmospheric Dust Spot Efficiency".

Air filter efficiency can be expressed as

μe = nt / nu = (nu - nd) / nu                                  (1)


μe = air filter efficiency

nt = particles trapped

nu = particles upstream

nd = particles downstream

Air Filter Arrestance

Arrestance is a measure of the ability of an air filtration device to remove synthetic dust from the air.

The arrestance describes how well an air filter removes larger particles - such as dirt, lint, hair, and dust. ASHRAE arrestance is a measure of the ability of a device to remove ASHRAE dust from test air.

The dust holding capacity of a filter is the amount by weight of standard dust the filter will hold without exceeding the resistance 0.18 in W.G. for low-resistance filters or 0.50 in W.G. for medium-resistance filters and 1.0 in W.G. for high-resistance filters.

Filter dust arrestance can be expressed as

μa = 1 - Ca / Cb                                     (2)


μa = dust arrestance

Ca = dust concentration after filter

Cb = dust concentration before filter

Related Topics

  • Ventilation Systems

    Design of systems for ventilation and air handling - air change rates, ducts and pressure drops, charts and diagrams and more.

Related Documents


Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

We use a third-party to provide monetization technologies for our site. You can review their privacy and cookie policy here.

You can change your privacy settings by clicking the following button: .


This page can be cited as

  • The Engineering ToolBox (2005). Air Filters - Arrestance and Efficiency. [online] Available at: [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter