Gavin Ó Sé
Bibliographic info:
10th International BUILDAIR Symposium, March 31/ April 1, 2017, Hannover, Germany

Purpose of the work

To describe the effectiveness of the thermal anemometer device in assisting airtightness testers to evaluate leakage zones, and specific leakages.

Method of approach

There are two main aspects:

While the building is pressurised to 50Pa use is made of internal doorways to close off each room to make a 'zone', and an airspeed reading is taken at the same location in the doorway for each door. Most doors are of the same size, therefore a good overview can be obtained of which spaces have the greatest air leakages.
On the basis of this then areas can be targeted for more specific leakage detection. Here also using the thermal anemometer some idea of the severity of the leakages can be obtained.

Content of the contribution

The thermal anemometer can be used to measure airspeed in a very small discrete location. It can also be used with various hoods or covers to give a volumetric airflow from e. g. ventilation systems or vents. For the purposes of zonal leak detection it can be used very simply with doorways, to allow a picture to be formed of the approximate leakage rates from various zones in a building. On the assumption that doorways are all much the same size, direct comparison can be made of airspeeds at the doorway, and simplistically, the higher the airspeed, the leakier the space inside that doorway.

In many buildings, the readings are taken at shoulder level, with the door just closed on the sensor end of the anemometer; for very airtight buildings this will not work, as most readings will be 0 m/s or very nearly. In this case, assuming the gap at the foot of the door is the same across doors, the anemometer is placed at the same location at the foot of each door to get the readings. Typically, all readings are taken when the fan equipment is generating the same pressure across the building, usually 50 Pa.

An example of a zonal inventory is as follows:

DownstairsAir Speed at Door (m/s)UpstairsAir Speed at Door (m/s)
Kitchen/Living 3.4Guest bed 1.74
Utility2.45guest ensuite 0.54
Sitting Room 0.4Girls0.73
Under Stairs0.0Bathroom2.81
  Spare room0.39

Once the zones have been recorded, then individual leakages can be sought and measured with the thermal anemometer, to see if these can be prioritised in turn. Separately, use of the thermal anemometer is useful in demonstrating a level of airflow to skeptical clients who may not be able to feel any leakages with their hands.

Results and assessment of their significance

It has been found that the method allows a type of inventory to be made on a room by room or space by space basis that can assist in both understanding leakage locations/severity and helping to prioritise the efforts to locate the leaks. The method has its limitations - it does not work for spaces open to the fan equipment and is more qualitative than quantitative, although it does allow an idea to be gained of the 'order of magnitude' of leakage in the various areas.


The thermal anemometer is a useful device to approximate zonal leakage patterns when used in conjunction with fan pressurisation of a building that has the internal spaces closed off into discrete spaces. It can allow a more informed approach to the setting of priorities for rectification, as well as a means of checking if rectification has been effective, by repeating the checks after fixes.


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