The image below shows the cross-section of a house and illustrates the measurement principle. The blower door is placed in the exterior door on the ground floor (shown here by the red arrow pointing from inside to outside). The blue arrows (pointing from outside to inside) indicate the leaks that are detected when the building is depressurised.
With the blower door, the air tightness of buildings is assessed by determining the N50 value. This indicates how many times the total air volume of a building is exchanged in one hour at a pressure difference of 50 pascal. A pressure difference of 50 pascal is comparable to a wind pressure on the facade of 4 to 5 Beaufort.
