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MVHR Commissioning in Irish Homes – Requirements, Certificates and Real-World Practice
Mechanical Ventilation with Heat Recovery (MVHR) is now standard in many new-build homes in Ireland. However, without proper MVHR commissioning, even a high-quality unit and duct system can lead to noise, stale air, excess humidity and unhappy homeowners.
In reality, MVHR commissioning in Ireland is not just a “nice to have”. It is the step that shows the system matches the design, complies with ventilation standards and actually delivers the right airflow in each room. As installers, our role is to test, balance and document the system so that the design team, BER assessor and Assigned Certifier have the evidence they need.
This guide explains how MVHR commissioning typically works in an Irish dwelling, what is measured on site, how commissioning links to validation, and the common mistakes we see in everyday projects.
What does “commissioning” actually mean for MVHR systems?
In simple terms, MVHR commissioning is the process of confirming that the installed system:
- Matches the system design (room-by-room airflow rates, duct types, unit model and controls).
- Achieves the required extract and supply MVHR flow rates at every terminal.
- Operates quietly and efficiently at both normal and boost speeds.
- Is documented clearly so that building control, BER assessors and the homeowner can understand the results.
It is much more than just turning the unit on or checking that “some air is coming out of the vents”. Instead, it is a structured test-and-balance process, backed up by a commissioning sheet and, on many projects, a separate validation certificate prepared by an independent validator.
When is MVHR commissioning used in Ireland?
On most new dwellings that aim for NZEB / Part L performance and use MVHR or MEV to comply with Part F, commissioning is simply part of the job. The design team relies on commissioning results to show that the installation does what the drawings and specifications promised.
The main reference document is Technical Guidance Document F – Ventilation (2019), published by the Department of Housing, Local Government and Heritage. This guidance sets out minimum airflow rates, example systems and compliance routes for domestic ventilation.
Testing methods for residential systems are aligned with I.S. EN 14134:2019 – Ventilation for buildings – Performance measurement and checks for residential ventilation systems. This standard is also referenced in the NSAI Ventilation Validation Registration Scheme as the benchmark for residential ventilation testing.
In practice, even if a local authority does not explicitly ask for every sheet, most well-run projects expect a completed commissioning sheet and supporting records as part of handover. Without them, it becomes harder for the professional team to sign off the house.
Does MVHR commissioning apply to Retrofit and Renovations?
Absolutely. It is a common misconception that rigorous commissioning is only for new builds. If you are undertaking a Deep Retrofit—especially one funded by SEAI grants or managed through a One Stop Shop—proper ventilation commissioning is just as critical.
When you upgrade insulation, replace windows, or improve airtightness, you are likely triggering the requirement for “Major Renovation” compliance under Technical Guidance Documents F and L. In these airtight, retrofitted homes, the ventilation system becomes the primary set of “lungs” for the building.
Furthermore, if you are aiming for a specific BER rating to release SEAI grant payments, the BER assessor will require evidence that the ventilation system is performing efficiently. Without a valid commissioning sheet (and often independent validation), you may face delays in signing off the project or receiving your grant funding.
Pre-commissioning checks (before you touch a flow hood)
Before any readings are taken, a competent person should carry out a simple but thorough visual and functional check. Otherwise, balancing can turn into a fight against basic installation faults.
Typical pre-commissioning checks include:
- Ductwork installation – correct sizes, no crushed flexible duct, no sharp or unnecessary bends, airtight joints and insulation where required.
- Filters and heat exchanger – filters clean and fitted correctly, heat exchanger seated properly, condensate drain installed with the correct fall and tested.
- Fan unit settings – correct MVHR unit model, correct supply voltage, right hand/left hand configuration, and the right spigots connected to supply and extract ductwork.
- Boost controls – bathroom switches, humidity or CO₂ sensors, and kitchen boost all wired, labelled and functioning.
If obvious issues are found at this stage, they should be fixed first. Otherwise, the system may never reach design airflows, no matter how long you spend on the valves.
Step-by-step MVHR commissioning process
During MVHR commissioning and airflow balancing, the first task is to identify the index terminal – the valve at the end of the duct run with the highest resistance (usually the longest route with the most bends and fittings). Typically, this terminal should remain as open as possible. You then set the fan speed so that this index terminal achieves its design airflow, and progressively throttle the other terminals until each one also hits its target.
1. Confirm design airflow rates
Start with the MVHR system design schedule:
- Extract and supply rates for each room.
- Design basis, usually Irish TGD Part F examples plus any project-specific requirements such as airtightness or occupancy patterns.
If no design schedule exists, you must calculate minimum airflow rates before you begin balancing. Otherwise, you cannot prove compliance with Irish ventilation standards or issue a meaningful ventilation validation certificate later.
2. Set base speeds on the unit
Using the unit’s control panel or commissioning software:
- Set the normal (trickle) speed to deliver the total required continuous ventilation rate.
- Set the boost speed to achieve the high-rate extract from all wet rooms (kitchen, bathrooms, WC, utility).
Record these fan percentages or duty settings clearly on the MVHR commissioning sheet. This information is important for future servicing and troubleshooting.
3. Measure and balance extract airflows
Next, measure the extract MVHR flow rates. Using a calibrated flow hood or vane anemometer:
- Measure extract airflow at each bathroom, WC, kitchen and utility valve with the system running at normal speed.
- Adjust valve positions until each room meets the design rate.
Because Irish regulations specify minimum airflows, it is best practice to aim for a tolerance of -0% / +10% against the design value. A result lower than the design rate may technically breach Part F compliance and may not pass independent validation.
Then:
- Repeat the process with the system at boost speed and confirm that high-rate extracts are achieved in wet rooms.
Every reading should be logged, because these figures form a core part of the commissioning sheet and the evidence base for validation.
4. Measure and balance supply airflows
After extract balancing, repeat the process for all supply terminals in habitable rooms (living areas, bedrooms, study).
- The total supply rate should match the total extract rate, so the system is balanced overall.
- If the unit cannot deliver design supply and extract rates at reasonable fan speeds, the issue usually lies with the MVHR system design or duct layout, not with the commissioning itself.
Again, record all measured MVHR flow rates on the commissioning sheet.
5. Noise, power and functional checks
Finally, carry out a set of functional checks:
- Confirm that noise levels in bedrooms at normal speed are acceptable for users.
- Check summer bypass operation where fitted, so that the unit can help reduce overheating.
- Verify that boost is activated correctly from all switches and sensors and that indicators on the controller behave as expected.
Where required by the project, you may also record fan power, specific fan power (SFP) or other performance metrics for Part L assessments.
Commissioning vs Ventilation Validation – how they fit together
On dwellings covered by TGD Part F 2019, there is often a second layer on top of normal commissioning: ventilation validation.
From the installer’s point of view, commissioning is the work done on site – balancing, setting up, measuring and filling in the paperwork. Validation sits above that. It is carried out by a person who is independent of the installation company and who checks whether the overall result meets the requirements.
In Ireland, this independent role is formalised in the NSAI Ventilation Validation Registration Scheme. A validator registered with NSAI (or an equivalent competent person) typically:
- Reviews the ventilation design and supporting documents.
- Spot-checks or witnesses some of the airflow measurements.
- Confirms that the system and documentation meet the minimum requirements of Technical Guidance Document F.
The output from that process is a Ventilation Validation Certificate. It is separate from, but based on, the installer’s commissioning records.
So, in simple terms:
- Commissioning (installer) – sets the system up, balances airflows and documents the results.
- Validation (independent) – uses these results, plus extra checks, to confirm that the dwelling meets the regulatory standard.
Building Regulations Part F Ventilation Commissioning sheet vs certificate
As Irish homes become more airtight, a well-designed, correctly sized and properly commissioned ventilation system is essential for comfort, health and energy efficiency. It is also a key part of domestic ventilation compliance under Building Regulations Part F – Ventilation (TGD F 2019).
One piece of paperwork that often gets forgotten is the ventilation commissioning sheet. This is the form recommended alongside TGD F for recording airflows, settings and basic system details.
What the ventilation commissioning sheet actually does
The commissioning sheet is effectively the installer’s record of what was done on site. It typically includes:
- Airflows measured in each room.
- Fan speed settings for trickle and boost.
- Terminal locations and identification.
- Notes on door undercuts and air transfer.
- Unit details, filters, condensate and access.
On many projects, installers are expected to leave this sheet with the client and the design team. Unfortunately, it is still common for homeowners never to see it.
A simple way to avoid confusion is to use the official Part F 2019 ventilation commissioning sheet (Department of Housing, Local Government and Heritage template – Eco Vent copy). Hosting this on your resource page allows architects, builders and homeowners to download the correct form and see exactly what should be filled in.
It is important to remember that this commissioning sheet is not the same thing as a validation certificate. The sheet records what the installer has set up and measured; a Ventilation Validation Certificate comes later from the independent validator, based on those records and additional checks.
Why a good design still matters on MVHR commissioning day
By the time commissioning happens, most key decisions have already been made. If the design was weak, the commissioning visit can turn into firefighting. A robust MVHR system design usually:
- Sizes the unit properly for the dwelling’s volume, expected occupancy and pressure losses in the ductwork.
- Sets room-by-room design airflows that follow TGD F 2019 examples and can be achieved at realistic external static pressure.
- Chooses duct routes and diameters that keep resistance low, avoid sharp bends and reduce noise and cross-talk.
- Documents all of this clearly so that the installer knows what to aim for, and the validator knows what to check.
Without that foundation, even a premium MVHR unit can struggle to meet compliance or may have to run at high speed just to reach the minimum airflows.
Three topics that often get brushed under the carpet
On real sites, a few issues come up again and again. They are not glamorous, but they make a big difference to both performance and compliance.
- Door undercutting (10 mm above finished floor)
For air to move freely between rooms, internal doors need a gap at the bottom – typically about 10 mm above finished floor level. This is one of the small details that show up on a commissioning sheet. Because it involves extra carpentry, it is sometimes left out. When that happens, flows between rooms are restricted and the system can struggle to behave as designed. - Anemometer and hood calibration
Airflow measurement relies on instruments being accurate. Good practice is to calibrate vane anemometers and flow hoods at regular intervals (for example, annually). If this is ignored, readings can drift, which means the figures written on the commissioning sheet may no longer reflect reality. That, in turn, can create problems when an independent validator checks the system. - Service access to the unit
MVHR units need regular filter changes and occasional maintenance. If a unit is pushed into a tight attic corner with no flooring or safe access, nobody will be keen to work on it. Good installations allow a safe platform, decent working space around the unit and easy access to the front panel. This makes long-term performance and compliance much more realistic.
Common commissioning mistakes in Irish homes
In day-to-day work across Ireland, the same patterns appear again and again:
1. No proper design – only “rule of thumb” settings
Without a calculated design airflow schedule, it is very hard to show that the system meets Irish ventilation standards. Balancing becomes guesswork and any commissioning certificate or report has limited value.
2. Trying to “fix” bad ductwork with commissioning
If ducts are undersized, full of sharp bends or poorly sealed, the system will often be noisy and still fail to reach design airflows. No amount of valve adjustment will make such a layout behave like a well-designed system.
3. Balancing only at boost speed
Some systems end up balanced only in boost mode. In normal (trickle) operation, flows may then be far from the design values. Because the house spends most of its time in trickle, this is the mode that really matters for comfort and indoor air quality.
4. No documentation
A verbal “it’s grand” does not help a BER assessor, Assigned Certifier or future buyer understand how the system was set up. Without a commissioning sheet and, where applicable, a validation certificate, it is difficult to prove what was actually delivered.
5. Ignoring Specific Fan Power (SFP)
Hitting the airflow targets is only half the story. If fans are forced to run at 80–90% speed to overcome poor ductwork, the Specific Fan Power (SFP) can easily exceed the limits assumed in DEAP under Part L. Measuring fan power and SFP helps to show that the system is not only compliant, but also reasonable to run in everyday use.
How good projects usually handle commissioning and validation
On well-managed builds, the different roles fit together roughly like this:
- The designer produces an MVHR layout and airflow schedule that follow TGD F and Part L guidance.
- The installer follows that design, installs the system, commissions it, and completes the ventilation commissioning sheet with measured airflows and settings.
- The independent validator (for example, NSAI-registered) reviews the design and commissioning records, carries out their own checks and issues a Ventilation Validation Certificate where required.
- The homeowner receives the full ventilation pack – design info, commissioning sheet, user guidance and, if applicable, the validation certificate.
From the installer’s side, good documentation and stable readings make life easier for everybody further up the chain.
Need help with MVHR commissioning in Ireland?
If you are building or renovating a home in Ireland and need MVHR commissioning, it helps to have a team that understands both the regulations and the practical realities on site. A specialist installer can:
- Review the MVHR system design and duct layout before final fix.
- Carry out on-site testing, balancing and full MVHR commissioning in line with I.S. EN 14134:2019.
- Provide a complete ventilation commissioning sheet
- Prepare documentation and data so that an NSAI Registered Ventilation Validator can issue a Ventilation Validation Certificate where required.
When commissioning is done carefully, the result is simple: quieter operation, better air quality, clearer paperwork and a smoother path through compliance.