Air flow rate testing and commissioning of ventilation systems

4.1 Mechanical ventilation systems must be commissioned to provide adequate ventilation. A commissioning notice must be given to the building control body.

4.2 Air flow rates for mechanical ventilation in new dwellings must be measured. A notice of the measured air flow rates must be given to the building control body.

NOTE: Paragraphs 4.1 and 4.2 apply to intermittent extract as well as continuous mechanical ventilation systems.

4.3 The person responsible for commissioning should complete air flow measurement test and commissioning sheets including, as a minimum, all information in Part 3 of the example sheet given in Appendix C.

NOTE: When mechanical ventilation is commissioned, the use of fuel and power should also be considered in accordance with Part L of the Building Regulations (L1(b) of Schedule 1). Installers may provide notice of commissioning to cover Part F (F1(2) of Schedule 1) and Part L in the same document.

Inspection standards

4.4 Ventilation systems should be inspected and tested in accordance with paragraphs 4.5 to 4.12.

Background ventilators and intermittent extract ventilation

4.5 For background ventilators, all of the following measures should be undertaken and the results recorded using the checklist in Appendix C.

a. The minimum equivalent area for background ventilators from Table 1.7 should be identified and recorded.

b. The actual equivalent area and location of installed background ventilators should be recorded.

c. Checks should be made to determine that the background ventilator controls work and that they open and close correctly.

d. The quality of the installation of the ventilator product should be checked to ensure it is
correctly mounted within the wall or window aperture.

4.6 For intermittent extract fans, the installer should carry out checks to establish the following.

a. That the fans operate correctly.

b. That the fans respond correctly to the controls provided with the installation.

c. That any run-on timers are set to at least 15 minutes.

Ducted systems

4.7 For all ductwork and terminals, the following checks should be made and the results recorded in the checklist in Appendix C.

a. That the system has been installed to achieve both of the following.

i. The design criteria.

ii. A standard that will not reduce its performance.

b. That the number, size and location of the air terminals provide effective air distribution in the space.

c. That all ductwork and terminals are in good condition with no obvious defects that will affect the performance of the system.

d. That the air flow direction is correct at each room terminal.

e. That there are no abnormal noises from the ventilation system, including in all of the following situations.

i. On start-up.

ii. When running in background ventilation mode.

iii. When running at the high rate.

4.8 For continuous mechanical ventilation systems, such as continuous mechanical extract ventilation or mechanical ventilation with heat recovery, the system should be balanced to achieve design air flow rates at each room terminal. The fan manufacturer’s instructions should be followed when balancing the system. If specific details are not available from the manufacturer, the relevant set of instructions from sub-paragraphs (a) to (e) below should be followed.

a. For adjustable terminals with a fixed (stepped) speed fan, the following apply.

i. The fan speed should be set to achieve the desired continuous flow rate.

ii. The index terminal flow rate should be set with the terminal fully open and all other
terminals should be adjusted to achieve the required flows at each terminal.

iii. If the total flow rate cannot be achieved through all the terminals, then the fan speed
should be increased.

iv. If all the terminals have to be set to a significantly closed position to achieve the required
air flow rate, then the fan speed should be reduced and the terminals rebalanced.

b. For adjustable terminals with a controllable speed fan, the following apply.

i. The fan should be set at a speed that will approximately achieve the desired continuous
flow rate.

ii. The index terminal flow rate should be set with the terminal fully open and all other
terminals should be adjusted to achieve the required flows at each terminal.

iii. If the index terminal has to be set to a significantly closed position to achieve the required air flow rate, then the fan speed should be reduced and the terminals rebalanced.

c. For fixed terminals with flow adjustment by duct damper or a similar device at the fan unit, the guidance in sub-paragraphs (a) or (b) above should be followed, depending on the type of fan speed control.

d. For adjustable terminals with a fixed-volume flow fan, the following apply.

i. The fan speed should be set to achieve the desired continuous flow rate.

ii. The index terminal flow rate should be set with the terminal fully open and all other
terminals should be adjusted to achieve the required flow rates at each terminal.

NOTE: Adjusting the terminals only balances the flow. Total flow rate is governed by the fan
control setting. Care should be taken not to close the terminals too far, because the fan unit
will always maintain a constant volumetric flow rate. Closing the terminals will require the fan to work harder to achieve a given air flow rate.

e. For fixed terminals with automatic flow adjustment at the fan unit, the fan speed should be set to achieve the desired continuous flow rate. The flows are balanced by automatic devices within the fan unit, so cannot be adjusted.

Air flow rate testing

4.9 The air flow rate of all mechanical ventilation fans should be tested. This includes any of the following.

a. Intermittent extract fans.

b. Cooker hoods.

c. Continuous extract fans and/or terminals.

d. Continuous supply fans and/or terminals.

4.10 A calibrated air flow device with a proprietary hood should be used to measure the air flow rates at each room terminal following the procedure detailed below.

a. The design air flow rates should be determined in accordance with Table 1.2.

b. Both of the following should be confirmed.

i. All intended background ventilators or other air transfer devices are open.

ii. All internal and external doors and windows are closed.

c. Air flow measurements should be performed using an air flow device that complies with all of the following.

i. Has a proprietary hood attachment.

ii. Has an accuracy of ±5%.

iii. Has been calibrated within the last 12 months at a calibration centre accredited by the
United Kingdom Accreditation Service (UKAS).

d. The air flow for each extract/supply fan or terminal should be recorded in litres per second (l/s) on the commissioning sheet (see Part 3 of Appendix C).

NOTE: In exceptional circumstances, the configuration of some fan units may prevent air flow rates from being measured. If so, evidence should be provided to assure the building control body that the flow rate can be determined by following the manufacturer’s guidance.

Controls

4.11 The correct operation of each control function should be tested where it is practical. Ventilation controls should be inspected to ensure that the following have been achieved.

a. All local controls have been installed in accordance with the manufacturer’s instructions.

b. All local controls are adequately labelled to clearly indicate their function.

c. If sensors have been installed separately from the fan unit, that the manufacturer’s installation instructions were followed.

d. Where control of the fan is automated, that the controls are configured to ensure that
automatic controls do not disturb occupants; for example, by sudden changes in fan speed.

4.12 If manual controls are provided, clear and detailed instructions should be given to the occupier as part of the information package described in paragraphs 4.13 to 4.17.

Operating and maintenance instructions

4.13 Sufficient information about the ventilation system and its maintenance requirements must be given to the building owner to allow the system to be operated effectively. This should include both design flow rates and maintenance requirements. The information should be provided in a clear manner, for a non-technical audience.

4.14 A copy of the completed commissioning sheet in Appendix C should be given to the owner of the dwelling.

4.15 The operation and maintenance information should contain specific instructions for the end user on how and when to use the ventilation system, including information on the intended uses for the available fan settings. Information should also be provided to suggest when, and how, the system components should be cleaned and maintained.

4.16 The following information should be provided where relevant.

a. Manufacturer’s contact details.

b. That background ventilators allow fresh air into the home and should be left open.

c. The location of automatic controls and how to set them.

d. The location of manual controls for the on/off and high rate settings for a mechanical
ventilation system and how to use them.

e. How cleaning and maintenance of the system and its components should be carried out.

This includes the location and specification of filters and how to assess when to replace filters.

f. How to access ducts for cleaning, how to undertake cleaning of plant and ducts and the
intervals at which cleaning should be undertaken.

g. The location of sensors and how to recalibrate them.

h. Design flow rates.

4.17 The operation and maintenance information should also contain relevant manufacturers’ literature, including the following, where relevant.

a. Component specifications.

b. Installation guidance.

c. Operating instructions.

d. Maintenance schedules.

e. Guarantees.

f. Registration card.

g. Spare parts lists.

h. Instructions for obtaining spare parts.

Home User Guide for new dwellings

4.18 A Home User Guide should be provided for a new dwelling as described in Section 9 of Approved Document L, Volume 1: Dwellings. It should contain a section on ‘Ventilation’ that provides nontechnical advice on the ventilation systems provided within the new dwelling.

4.19 The Home User Guide is in addition to the operating and maintenance instructions. It is intended to be a non-technical overview for the occupiers, and should include some basic details on the operation and maintenance of the system. The operating and maintenance instructions provide further details as required.

NOTE: Information about overheating and the conservation of fuel and power are required
under different regulations and guidance is given in Approved Documents O (Overheating) and L (Conservation of fuel and power). Where the system provides more than one function, the owner should be informed of each separate function.

Additional information for work in existing dwellings

4.20 When new ventilation is installed in an existing dwelling, information about it should be provided to the building owner in accordance with paragraphs 4.13 to 4.17.

Example text on the purpose of ventilation and the standards for existing dwellings can be viewed at https://www.gov.uk/government/publications/home-user-guide-template.

However, there is no requirement to follow the layout, format or text used in the example.

Section 4: Commissioning and providing information