Extract Fan Testing

Who needs extract fan flow rate testing? Under Part F of the Building Regulations, every fan in every house needs testing for new build dwellings.

If you have a Warranty provider (e.g., NHBC, Premier, LABC etc.) these may also request the extract fan flow rate testing reports even if Building Control do not.

What is extract fan flow rate testing? (Also known as Air flow rate testing and commissioning of ventilation systems). This is the process of running the fan at and measuring the flow rate with a measurement tool, in our case an Anemometer.

For example, if you have an intermittent fan (comes on with the light) in your bathroom, then it needs to achieve 15 litres/second. We would measure the fan to see if this rate is achieved.

The purpose is to ensure the target flow rate is being achieved in practice to reduce risk of build of moisture, smells, condensation and help maintain good indoor air quality.

The mechanical extract fan system also relies on required levels of background and purge ventilation. This is often achieved through trickle ventilators in your window heads and openable windows. The required opening sizes should be determined by the designer in accordance with Part F of the Building Regulations and communicated to the window supplier to ensure this target is met.

Our qualified extract fan flow rate tester will be in touch to confirm the agreed date and time for the air tightness test.

We will check and if required, advise on the following:

• What fans you have installed
• Confirm what date and time is convenient
• Provide extract fan flow rate checklist and guide to review and be ready for the air test
• If a fail occurs, then offer advice if a problem can be identified.
• Same day certificate release

Here are some common reasons for extract fan flow rate testing:

• Putting in the wrong fan. Such as a bathroom fan (15 litres/second) in a Utility Room which requires 30 litres/second.
• Check the flow rate of the fan and convert to litres/second
• If the extract fan has to be connected to a duct because you do not have an external wall, then this will reduce the flow rate. We recommend using an extract fan with a higher flow rate to overcome this.
• Check the ducts have been installed correctly before sealing up. Ensure no damage or blockages.
• We recommend avoiding flexible hoses. These cause issues. Easier for the installer, but causes problems for you. Try and use rigid ductwork.
• Check the external grille is suitable and not blocked.
• Make sure the flow rates are clearly communicated.
• If you have a cooker hood extracting direct to the outside air, then this needs 30 litres/second. However, if you have a fan going through the wall, then this needs 60 litres/second.
• Ensure your fans are all the same type. For instance, if using continuous running fans, then all fans need to be the same type 9continuous) including the kitchen fan.
  Ensure the trickle ventilators on your windows have been sized correctly and they window suppliers know the target and have added them to confirm in writing they have been provided.
• Check each fan has power to it.

Low Carbon Box have a good understanding of the whole house specification with nearly years in architecture, energy and site testing.

Our extract fan flow rate tester is qualified and we use UKAS calibrated air flow measurement equipment in line with Part F of the Building Regulations.

We provide upfront checklists to help you pass and offer a significant discount when using our air tightness testing service.