MVHR commissioning

What is MVHR commissioning?

Commissioning is setting up a ventilation system and measuring that it delivers the required air flow rates at each terminal, then recording the results. For MVHR it means balancing the supply and extract, measuring the flow, and checking it against the Part F rates for the home. It confirms the system works as designed, not just that a unit was installed.

A system can be perfectly installed and still fail to deliver the right airflow if it was never balanced, or if a duct is crushed or too long. Commissioning is the check that turns an installed system into a proven one, with figures on paper rather than an assumption that it works.

Does Part F require MVHR commissioning?

Yes. Under the Building Regulations, mechanical ventilation air flow rate testing must be carried out to an approved procedure, and notice of the results given to the building control body. The results must be recorded and given to the local authority no later than five days after the final test. Commissioning is a legal step, not an optional extra.

The requirement sits in the regulations that accompany Approved Document F. Separately, the person carrying out the work must give the owner sufficient information about operating and maintaining the ventilation system within five days of the work being completed. So both building control and the homeowner should receive documentation.

Sources: GOV.UK

What does the MVHR commissioning process involve?

An installer or commissioning engineer sets the fan speeds, then measures the actual air flow at each supply and extract terminal using calibrated equipment, adjusting until the system delivers the required rates. The measured figures are recorded on a commissioning sheet, based on the one in Appendix C of Approved Document F, which goes to building control.

Balancing matters because the flow at each terminal depends on the length and shape of its duct run, so terminals furthest from the unit need adjusting to match those closest. A properly balanced system delivers the right air to every room; an unbalanced one over-ventilates some rooms and starves others.

Sources: GOV.UK

Who can commission an MVHR system?

Commissioning should be done by a competent person with the right calibrated equipment, often the installer or a specialist commissioning engineer. Some work through a competent person scheme, which lets them self-certify without a separate building control inspection. Either way, the measured results have to be produced; a system that is not properly commissioned may not pass.

A self-builder can commission their own system in principle, but it needs the correct airflow measuring equipment and knowledge of the Part F procedure, so many bring in a specialist. The important thing is that real, measured figures are recorded and submitted, not estimated.

Why does commissioning matter to a homeowner?

For a homeowner, the commissioning record is the proof that the ventilation actually works, not just that a unit was fitted. A system can be installed and still under-perform if it was never balanced or if ducting is crushed or too long. Ask for the commissioning sheet: it is your evidence of a compliant, working system, and you should also receive information on operating and maintaining it.

If you are buying a new build or having MVHR installed, the commissioning sheet is a document worth keeping. It records the measured airflow against the required rates. Without it, you have no independent evidence the ventilation performs, which can matter for comfort, for air quality, and if you ever sell.