Airflow | An Extracting Science

Airflow | An Extracting Science

John Kelly, Marketing Manager at Airflow Developments, discusses the importance of installed performance, correct installation and commissioning of extractor fans in preventing ineffective ventilation.

In an effort to make UK homes more energy efficient, new builds are becoming increasingly well insulated and, as a result, are essentially sealing the home, preventing airborne pollutants and excess moisture from escaping which can develop into Toxic Home Syndrome.

Breathing easy
For a new home to meet the latest Building Regulations there must be a ventilation system installed as prescribed in Approved Document F1, Means of Ventilation. This is to ensure that excess moisture created through every day living like breathing, cooking, showering, and indoor air pollutants arising from textiles, furniture and aerosols, which are potentially harmful to both occupants and the fabric of the building, are properly extracted.

However, electricians should be aware that while some ventilation manufacturers claim that to have products that comply with the latest Building Regulations, in some cases the performance might only be in regards to a free air environment. Therefore a fan may not perform to the required standard when installed as part of a system, which can lead to a build-up of moisture and pollutants over time.

Installed performance
When looking for an extractor fan, electricians should check the installed performance data – a simple guide to this is to look at the fan’s performance graph.

By using a provisional system pressure of 10 Pascals, electricians will have a good estimate as to how the fan may perform when it’s installed in the home; dependent upon the ducting system.

For installation advice, the Domestic Ventilation Compliance Guide provides tips that can help avoid an incorrectly installed system that can severely impact the performance of a fan. For example, if flexible ducting is being used, it needs to be pulled taught to 90% of its maximum length and cut to a suitable length, as squashed up and crushed flexible ducting creates increased system pressure that a fan cannot overcome, meaning the required installed ventilation rates are not met. By establishing ducting is clear of dust and debris and that the exterior grille has the required 90% free area, electricians can ensure that a fan will achieve the required installed performance.


How to test
To test a fan for installed performance electricians should use a powered air flow meter. These instruments use an inbuilt fan to equalise the back pressure of the measuring device so that accurate air flow measurements are possible without further complex calculations – this should be carried out on-site by an assessed and registered ‘Competent Person’ who has completed an approved ventilation installer course, such as NICEIC training.

Furthermore, on-site testing should follow a ‘Best Practice’ process and adopt air flow measurement, Method A – The Unconditional Method – using a suitable UKAS certified measuring instrument, generically referred to as a ‘Powered Air Flow Meter’ or ‘Zero Pressure Air Flow’. Further information on this method can be found in NHBC Building Regulations Guidance Note G272a 10/13 and BSRIA’s ‘A Guide to Measuring Air Flow Rates’ document BG46/2015.

For more details about the range of ventilation products from Airflow visit:

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