Ventilation systems include filters that reduce air pressure.
The amount of energy they consume depends on how much resistance the filter offers to air, with filters that offer a lower resistance consuming less energy. Energy-efficient filters create a lower pressure drop across them. A filter that offers a higher active surface area produces a lower pressure drop. Thicker, deeper filters also create lower pressure drops. The easiest way to monitor a filter's pressure drop is to measure it directly using a differential pressure gauge.
Plug the static pressure probe into the "low" port of the differential pressure gauge.
Plug the total pressure probe into the "high" port of the differential pressure gauge.
Hold the static pressure probe at a right angle to the flow of air from the filter.
Hold the total pressure probe parallel to the flow of air from the filter.
Read the pressure drop from the gauge.