Extract Fan Commissioning
6th November 2023
One of the most frequently asked questions we get is “Why are you asking for ventilation testing?” Well, as our previous blog showed, ventilation is essential to ensure the comfort and health of building occupants. However, experience has shown that over half of installed extract fans fail to meet Building Regulations.
Why Do We Need To Test?
Whilst you might think that the manufacturer’s rating on a fan should be reliable, the reality is often different. Manufacturers test their fans in optimal laboratory conditions. Once installed, fan performance can deviate substantially from these ratings. Real-world testing has revealed that fans, even those from renowned manufacturers, might not meet the advertised flow rate even in standard installation settings.
Why Do Fans Fail?
We have found that most failures are down to one of 3 reasons :
- Installation: Ensure that ducts aren’t squeezed, kinked, or forced to navigate around obstructions or sharp turns. Rigid ductwork is much more reliable than flexible “elephant trunk” ducting.
- Duct length: Ideally, position the fan as close to external air as possible as the length of the duct impedes the extract fan’s performance. Typically, if the run exceeds 1.5 metres, its efficiency diminishes drastically.
- Wrong fan: Make sure you specify a fan that is sufficiently powerful. Axial fans are fine for short duct lengths, but centrifugal or inline fans are generally better choices for longer duct runs.
So What Exactly Is It You Need?
We will ask you for a Ventilation Commissioning Certificate – also known as a Flow Rate Test; a Part F Test; a PEATA Certificate or an Airflow Test (this should not be confused with an Air Leakage Test which is completely different).
Ventilation Commissioning measures the volume of air being extracted through the fan and compares that with the performance requirement. There are different types of equipment that can be used, but the most common method is to use a specially-calibrated piece of equipment known as a ‘vane anemometer’ which comes with a hood that fits over the fan.
A vane anemometer in use
Who Does The Test And How Is It Done?
Typically, the test is carried out either by the electrician who installed the fan, or by a specialist ventilation testing and compliance company at the end of the project.
In the majority of cases, the testing of fixed fans will be carried out within the room served by the fan. However, where the ventilation is provided via a cooker hood it may not be possible to carry out the test from inside the room, so you may instead need to carry out the test on the outside of the dwelling.
All testing equipment used should be calibrated annually at a UKAS accredited laboratory.
What Happens If The Test Fails?
If a ventilation system fails the test, then it will be necessary to either replace the fan with a more powerful model and/or replace the ducting. This is likely to be a disruptive process especially if left until decoration is complete.
Given the financial and time implications, it’s prudent to make sure that you use the correct fan and use rigid ducting to enhance the odds of a successful first-time pass.
Flow Rate Tests are more than just a Regulatory requirement; they ensure that ventilation systems in buildings function optimally for the well-being of occupants. With the extension of the Defective Premises Act to include domestic extensions, being able to prove that the ventilation was installed and working correctly at the time of completion will be vital for contractors to defend claims made regarding condensation and mould occurring in the future.
Building Regulations are seen as a set of rules to be followed, which, yes, essentially, that is exactly what they are, but building regulations don’t need to constrict architects.
The Building Safety Act 2022 received Royal Assent on 28 April 2022, marking a monumental shift in the regulatory landscape for building safety in the UK.