Extractor fan flow rate testing

Extractor fan flow rate testing

Approved Document F of the Building Regulations requires that all mechanical extract fans in new dwellings must be subjected to a flow rate test. Evidence of this test must be passed to the Building Control Body (BCB) as part of their sign-off procedure.

There are three alternative methods which can be followed to test, record and report the testing of extractor fans. Using a Vane Anemometer, our testing procedure follows Method 3 – The minimum benchmark method.

AKG51H Close up of extractor fan above stainless steel pan on hob

How Energytest can help

RELIABLE – Building Regulations sign-off is often time-constrained and stressful. We shall attend site at a time that is convenient for you and provide certificates within 24 hours of the test.

VALUE – We offer discounted fees for any testing that is undertaken at the same time as an air leakage test.

ACCURATE – All our test equipment is UKAS calibrated.

SINGLE-SOURCE-SOLUTION – As well as testing the flow rate of extract fans, we can also provide:

SUPPORT – For added piece of mind our test engineers will be happy to assist you with free advice throughout the construction process.

SAFE – Like you, we take health and safety seriously. All of our engineers are CSCS certified.

Revisions to the regulations governing the energy performance of buildings have led to a requirement for airtight construction. Dwellings that achieve low air permeability rates have less heat loss through infiltration, and consequently, lower CO2 emissions. However, with buildings built airtight it is vitally important that adequate ventilation is installed. Insufficient ventilation can result in damp and condensation issues.

The purpose of an extractor fan flow rate test is to ensure that the system installed meets the minimum ventilation requirements of the Building Regulations.

Factors that affect the measured flow rate of an extractor fan include:

  • The rated flow rate of the fan as tested under factory conditions. For example, extractor fans that are designed for use within toilets will have a lower rated flow rate than those designed for use within bathrooms. Ensure the fans installed are designed for use within the rooms in which they are fitted. Where possible install fans with rated flow rates that well exceed the minimum level required for the rooms in which they are installed.

  • The length of duct runs. Long duct runs will result in a drop-off in fan performance.

  • The type of ducting installed. Where possible install rigid ducting. Flexible ducting can easily become ripped or crushed, preventing air flow.

  • Bends, kinks and obstructions to ducting will adversely affect fan performance. Where flexible ducting is installed it should be extended to 90% of its full length to ensure flow resistance is minimised.

  • Connections should be made using rigid connectors and jubilee clips.

  • External grilles should be clear of obstructions to allow a free flow of air.

The most common form of ventilation is referred to as System 1 – Background ventilators and intermittent extract fans. This is a decentralised ventilation system in which mechanical extract fans provide intermittent, rapid air extraction to each wet room within the dwelling.

The minimum flow rate for an intermittent extract fan varies depending on the type of room in which it is installed:


RoomMinimum flow rate
Kitchen (adjacent to hob)30 l/s
Kitchen (elsewhere)60 l/s
Utility room30 l/s
Bathroom15 l/s
Sanitary accommodation6 l/s

What our clients say:

“We have used Energytest for SAP compliance reports, Air Leakage testing and AD Part F ventilation fan testing over the last 5 years. They have provided an extremely efficient service and offered very clear and concise technical advice right through both design and construction process! Recent on-site air leakage and ventilation testing was carried out with real care to avoid any damage to recently decorated houses and remedial advice helped ensure a successful test.”

A Burrows – Counterpoint Properties Ltd