Blower Door test

Determination of the air permeability (air tightness) of buildings is an increasingly monitored parameter of construction today, especially for passive energy standard buildings. This property is often perceived as unnatural by the public, i.e., going against nature, and it is often believed that every building should “breathe”. This is, of course, true. However, the “breathing” should not be achieved by energy loss through the building envelope, but by ensuring adequate exchange of air based on natural window ventilation or other technical systems (mechanical ventilation with heat recovery, etc.). If the parameters in this area are not established directly (e.g., based on a subsidy programme), we recommend that requirements as regards the level of air tightness of the building should always be incorporated into the contract for work.

Consequences of failure to comply with the appropriate building air tightness requirements:

  •          increased heat loss
  •          reduced efficiency of mechanical ventilation systems
  •          increased risk of condensation in untight areas (both inside and on the surface of structures)
  •          reduced quality of indoor environment (mould, cold radiation)
  •          reduced life of structures
  •          deterioration of acoustic properties

The actual measurement of air permeability is most often performed using the pressure gradient method known as the Blower Door Test, in accordance with ČSN EN 13829. For this purpose, the Technical and Test Institute for Construction Prague (TZÚS Praha, s.p.) uses the Minneapolis Blower Door MultipleFan, a modern measuring device with three fans. With this system, we can diagnose both houses and large buildings (residential, industrial, administrative, etc.) with volume of internal air up to 450,000 m3, with air flow through fans of up to 22,500 m3 h-1.


The principle of the test is the creation of underpressure or overpressure in the building, using one or more BlowerDoor fans. Based on the detected values (air flow rate at the given pressure conditions, volume of internal air, etc.), “air exchange intensity in the building” is determined – n [h-1]. This parameter specifies how many times, at the given pressure difference, the volume of internal air in the building (or in the part that is subject to analysis) is exchanged in one hour. In practice, the most frequently used parameter to specify the level of airtightness is the air exchange intensity value determined at 50 Pa reference pressure difference, known as n50 [h-1]. In large buildings, the results can also be applied to the floor area (w50 [m3/(h.m2)]) or to the building envelope surface (q50  [m3/(h.m2)]).

Measurement is successfully performed after the completion of the airtight layer of the building (before the final covering of the structure) in order to effectively eliminate any defects. Identification of defects is also provided (anemometer, smoke generator, thermographic camera).

In this field, the Technical and Test Institute for Construction Prague also has facilities for determination of air permeability class of hole filling according to EN 12207. This diagnostics is also performed on site, focusing on embedded structural elements (windows, doors). Determination of the resulting class is then performed using the evaluation of total air permeability values in relation to the area of the building element [m3/(h.m2)] and the length of the functional joint [m3/(h.m)].


The Technical and Test Institute for Construction Prague is a member of the Blower Door Association CZ (, and it is approved by the State Environmental Fund of the Czech Republic as a specialist supplier of measurement for the Green Savings Programme.



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