Outdoor air may be ‘cleaned’ by filtration. This is a method by which particulates and, sometimes, gaseous pollutants are removed from the air. Pollutants are intercepted by a filter while allowing clean air to pass through. This method of air cleaning is especially necessary when high concentrations of particulates are present or when the source of pollutant is derived from outside the building. Potential benefits can include improved air quality, reduced dependence on ventilation and improved energy efficiency.

Measurements are needed to verify the performance of ventilation systems and to test the air-tightness of the building shell. They are essential for commissioning, diagnostic analysis, design evaluation and research.

Various units are used to describe the rate of ventilation. These include:

Volumetric flow rate: Ventilation and air infiltration is commonly expressed in terms of a volumetric air flow rate e.g. litres/s (l/s) or m³/s.

The Air Infiltration and Ventilation Centre's first glossary of ventilation terms was published in 1981 as AIVC Technical Note 5 and contained definitions of over 700 words relating to air infiltration and ventilation. Since then, many definitions have been updated and new terms have been added.