LISTEN...

The pressure gauge on a blower door system is called a 'manometer' (man-AW-mitter). It is used to accurately compare the air flow pressure from the fan, the pressure inside the building and the difference between inside and outside.

The manometer is connected to hoses running from the fan unit and running to the outside of the building.

Note the pressure of 50 pascals show on the readout - the number on the right side (shown below) is cubic feet per minute of air flow.