Ventilation is most effective when air is extracted close to the vapour source; bathroom, kitchen, drying clothes and occupied rooms. The internal ventilation does not meet Building Regulation 2010 Part F requirements. This is best achieved with mechanical extractor fans. See specifically P39 and P19:

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  1. Bathroom 15 l/s with a 30-minute overrun.
  2. Kitchen 30 l/s adjacent to hob; or 60 l/s elsewhere in kitchen.

Surveyors should use “anemometer on all surveys”

James Berry of PCA (“Property Care Association”).


  • If you are an expert, use Testo 417 Vane system with funnels £347.40.
  • If you are an occasional user or need a back up, buy Anemometer Handheld UNI-T UT363BT £26 (you have to make a calculation to work out the airflow in l/s based of the comparative aperture sizes (meter to vent). It at least tells you if there is any meaningful airflow, and comparative entry and exit airflows.
  • Often all you need to do is measure and compare flows in and out. You can say £320 buy using any meter, such as UNI-T UT363BT £26 and a large plastic ice cream carton or similar, large enough to cover (without obstructing) airflow from the bathroom and external vent. Cut a hole just big enough to measure with the anemometer. Compare. A difference of more than about 10% suggests a ventilation leak.
  • You can accurately calculate flow rates using cheaper anemometers, but they may not be accepted in court as reliable evidence.
  • All extractor fans should be tested inside and outside where the ducting isn’t short and straight. From February 2021, issues would not have been picked up without testing every fan (it only takes a few minutes).
    1. only 12% of fans were anywhere near Building Regs requirements – this is fine if windows are opened and doors closed to compensate.
    2. 8% had incomplete ducting which would not have been picked up without checking the ducting through to exit and where possible testing the exit extractor rate.
Bathroom extractor fan Feb 21
Results of testing all bathroom extractor fans on damp surveys in Feb 21

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