Air Flow Rate Testing of Ventilation

Air Leakage Testing Ltd undertakes vent testing of domestic ventilation for Approved Document F requirements. 

Ventilation is key in controlling moisture and pollutant levels in any home, if ventilation is insufficient it can mean poor air quality and mould development, leading, in the longer-term, to problems with the building and/or health issues.

Improved air tightness, as part of reducing energy consumption, needs to be balanced with appropriate levels of controllable ventilation.

Extract vents manufacturers claim a level of air flow based on laboratory testing this does not guarantee they will achieve this in practice due to various issues but most commonly the installation.

Therefore, Approved Document F Volume 1 ‘Ventilation’ requires background ventilation to be tested after installation as part of the commissioning process.

Part F stipulates requirements for different rooms depending on their usage and the type of ventilation.

  1. Vent testing for houses and flats, the requirements apply to extract ventilation in bathrooms, kitchens, toilets and utility rooms and/or mechanical ventilation in other habitable rooms.
  2. The requirements apply to new residential buildings, conversions, refurbishments and extensions.



Different vents are required to achieve different levels depending on the type of ‘System’ and the room’s purpose.

Air Leakage Testing Ltd undertake the air flow rate measurements using UKAS accredited equipment to determine whether each vent and the overall system complies with the requirements of Part F.

We provide extract vents test/commissioning certificate for each residential property that includes all the information required for compliance with Part 3 (Commissioning Details) of the Completion Checklist and Commissioning Sheet.

Background ventilators with intermittent extractors, these are the extract vents that come on with the light in the bathroom or when the cooker hood is switched on, they are used in combination with trickle vents in windows/doors.

Vents over the kitchen hob or in the utility room need to achieve 30l/s, bathrooms 15l/s, toilets 6l/s.

Continuous mechanical ventilation (MEV), these are the vents run at a ‘trickle’ all the time in bathrooms, kitchens, toilet, utility, etc but can run at a boosted level when required. 

There are required flow rates for boost in the wet areas and an overall rate based on bedroom numbers: Vents in kitchens or in utility rooms need to achieve 8l/s, bathrooms 8l/s, toilets 6l/s. The dwelling must have an adequate overall ventilation standard rate. This will depend on the number of bedrooms. For example, in one bedroom properties the overall standard ventilation rate must be 13 l/s. However, in five bedroom properties this rate must be 29 l/s for 5 bedroom properties.

Continuous mechanical ventilation with heat recovery (MVHR/HRV). This is where there are air supply vents in every room and also extract vents in the ‘wet’ areas.

There are requirements for individual fans on boost, a whole ventilation rate on trickle and a need for supply and extract to be balanced.

Our vent Testing Process

Air Leakage Testing Ltd undertake Part F air flow testing of extract vents for residential dwellings (houses and flats).

For Test Method C, the ventilation testing is carried out using a hood/cone placed over the extraction fan, which makes a seal with the area surrounding the fan/vent to channel the air from the fan/vent through a calibrated anemometer, which measures the air flow rate in litres per second.

If the air flow rate exceeds the required level for that room type it has passed. If the air flow rate is a little under the requirements for intermittent extracts in kitchens/utility rooms (above 24 l/s) and bathrooms (above 12 l/s), these are typically deemed to be satisfactory for Test Method C based on achieving these ‘benchmark’ targets given the limitations of site conditions which may mean that the maximum air flow rate may not be fully measurable.

A certificate including the information required for Part 3 of the Approved Document F (Volume 1) completion checklist is produced for each property. It lists the details of the property, equipment, test engineer and testing along with air flow extract rate results against the requirements for each fan and the overall system (where required).

The fans must be powered to conduct the test.

The testing is best completed in combination with air tightness testing or sound testing to minimise the costs (these services are also provided by Air Leakage Testing Ltd)


Common issues include:

  • Incorrect fan specification/selection – especially for use in the utility room where bathroom vents are often fitted but only have half the air flow capacity required
  • Incorrect set up of the extract fan – a lot of manufacturers produce fans that can run at high and low speeds with the default setting being low speed, this could mean that the air flow is much lower than required (often the low flow rate is around a third of the full capacity of the fan)
  • Incorrect installation, including:
    • Kinks in the flexible ducting/hosing
    • Concertinaing/compression of the flexible hosing which closes the opening of the ducting and restricts air flow
    • Poor connection between the ducting and the fan
    • Restriction of air flow at the external vent/grille/tile


As a result readings often fall below the requirements.

Often it is possible to identify and address the issue on the day of test and repeat the testing to achieve an improved result. 

What our clients say about us

“ALT were extremely helpful and knowledgeable. They worked with the site team to identify and resolve issues during construction.”
“I have used Air Leakage Testing Ltd on two separate occasions at my property and found them to be extremely thorough and professional at all times. The turnaround between site visit and subsequent reports was quick and efficient - making my life a whole lot easier! Would highly recommend to anyone!”

Established in 2002

5 Star Google Reviews


Why choose alt?

Helpful Engineers

We work with you to achieve the best result, identifying potential issues and repeating the testing once these have been addressed. We are on hand to answer any questions before, during and after the testing.

Flexible & Responsive

We aim to fit in with your chosen dates and times, to work around other trades and to minimise on-site disruption. Our lead times are typically a week but it may be possible to fit you in sooner. We issue quotes and certificates within 1 working day.


We have been air testing since 2002 and keep pace with changing regulations. All our test engineers hold ATTMA L1 registration and have considerable experience in undertaking tests and resolving potential issues.

Great value

Our efficient processes help us to offer very competitive prices. In addition, we can undertake air and sound testing on the same visit to save you more money. If you do receive a cheaper air testing quote, we will beat it.

Get a quote

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