Introduction
Commissioning is the part of an MVHR installation that is most often rushed, skipped or done poorly, and it is one of the most important. A system that has not been properly balanced will not deliver the right airflows to each room, may be noisier than expected, and will fail to meet Part F of the Building Regulations.
More importantly, improperly commissioned systems are frequently the cause of complaints from homeowners - reduced air quality, persistent humidity issues, condensation, and the sense that the system is not doing anything - even when the unit and ductwork are perfectly installed.
This guide explains what commissioning involves, what equipment is required, and what documentation Building Control needs to see.
What does commissioning actually involve?
MVHR commissioning is the process of measuring and adjusting airflows at every supply and extract valve in the system to match the design specification. The design will have set a target airflow (in l/s) for each room. Commissioning confirms the targets are being met and adjusts valve settings until they are.
At the same time, the total supply and extract airflows for the whole system are balanced - total supply should equal total extract to within approximately 10%.
When should commissioning take place?
Commissioning should be carried out after all ducting and valves are installed, all connections to the unit have been made, all supply and extract valves fitted at their final positions, and the building fabric is complete (plastering, decorating, fitted kitchens and bathrooms in place). The building should be in its normal occupied configuration - windows closed,
What equipment is needed?
Proper MVHR commissioning requires calibrated airflow measurement equipment. A digital anemometer with a suitable capture hood, or a pressure gauge with flow calculation, is the standard approach. The equipment must be calibrated and used correctly - different valve types require different measurement techniques.
- Digital anemometer or capture hood anemometer for valve airflow measurement
- Manometer or digital pressure gauge for system pressure readings • Installation drawings and the design airflow specification
- Unit manual for speed and setting adjustments
- Commissioning log sheet (required for Building Control handover)
Step-by-step commissioning process
Step 1 — pre-commissioning checks
Before starting measurements, visually inspect all ductwork connections, check that all valves are installed at their designed locations, and confirm that the unit is running at the correct voltage and rotating in the right direction. Check the filters are clean and correctly fitted.
Step 2 — set unit to design duty
Set the MVHR unit to its normal running (background ventilation) speed, corresponding to the design duty point. Check the unit manual for how to access and set speed modes.
Step 3 — measure extract airflows
Measure the airflow at each extract valve (kitchen, bathrooms, en-suites, utility room) using a capture hood or anemometer. Record each measurement against the design target.
Step 4 — measure supply airflows
Measure the airflow at each supply valve (bedrooms, living room, study, hall) in the same way. Record each measurement.
Step 5 — adjust and re-measure
If measured flows differ from design targets by more than 10%, adjust the valve settings and re-measure. Most valves have adjustable apertures or damper settings. Significant imbalances may require changes to unit speed settings.
Step 6 — check boost operation
Test the boost function (usually triggered by the humidity sensor or the wall switch). Confirm that extract flows increase as specified, and that supply flows respond accordingly.
Step 7 — document and hand over
Complete the commissioning log with all measured airflows, unit speed settings, date, and the name of the person carrying out commissioning. This documentation is required by Building Control.
What documentation does Building Control need?
Under Part F of the Building Regulations, the following must be provided to Building Control on completion:
- MVHR system design and flow rates to meet Part F regulations
- Commissioning log showing measured airflows at every supply and extract valve
- Confirmation that system performance meets the design specification
- Handover information for the building occupant covering system operation and filter maintenance
In practice, Building Control requirements vary between local authorities. Some accept a signed commissioning certificate; others want to see detailed airflow logs. Always check with your Building Control officer before commissioning.
If you require further information on commissioning, please call Epicair on 01892 600121 for advice on the right instruments for your project.
