Preparing to commission the mechanical ventilation system: essential checks before adjustments
Checking the installation: ductwork, tightness, condensate slopes, and accessibility
Before touching the settings, do a full walk-through of the ventilation ductwork. Ducts properly fixed, not crushed, with the right diameters. Check the tightness of the connections and the insulation of the ducts in unheated areas. On a balanced system, check the condensate slope, the trap, and the drainage. Keep easy access to the unit, the filters, and the inspection hatches.
Checking the vents and theoretical flow rates: kitchen, wet rooms, WC, living rooms
Make sure each vent is in the right place, clean, and matches the room. Compare the theoretical flow rates given in the manual or manufacturer's data sheet against the needs per room. The kitchen and wet rooms are on extraction. Living rooms receive the air inlets. Clear labelling avoids mix-ups before measuring with a flow meter.
A reminder of the 2026 compliance points: RGE, technical data sheets, manuals, and handover report
In 2026, keep a clean file. RGE qualification if subsidies are being used. Technical data sheets (unit, vents, ducts), up-to-date diagrams and installation instructions, including the DTU 68.3 rules. And a signed handover report with measured flow rates and any reservations noted. This is your safety net in case of an inspection.
Carrying out the basic settings on a balanced mechanical ventilation system: from power-on to speeds
Configuring the unit: speeds, modes (normal, boost), delays, and humidity sensing if present
After powering on, check the time and mode. Set the normal speed for daily use, then the boost mode for the kitchen or bathroom, with a delay (10 to 30 min depending on the unit). If your unit has a humidity sensor, choose a consistent threshold and test by simulating a rise in humidity.
Adjusting the extract and supply vents: dampers, sleeves, and labelling
Start by opening all the dampers. Then adjust vent by vent, aiming for the flow rates in the sizing plan. Mark the setting position on the sleeve and label each duct (kitchen, bathroom, bedrooms). Clear labelling avoids mix-ups during future maintenance.
Securing operation: rotation direction, noises, vibrations, and alarms
Check the fan rotation direction if access allows, then listen. Whistling, vibration, or humming often indicate a flow imbalance, a clogged filter, or a poorly fixed unit. Also check the filter and bypass alarms. If needed, check our guide on mechanical ventilation noise to identify common causes and fixes. A quick test beats a callback.
Balancing the mechanical ventilation flow rates: a field method for a stable balanced system
Measuring correctly: anemometer, measuring cone, pressure, and accounting for pressure losses
To adjust a balanced mechanical ventilation system, measure vent by vent with an anemometer and, if possible, a cone suited to the diameter. Let the network stabilise, make sure the filters are clean, then also note the pressure available at the unit. Bends, lengths, and silencers create pressure losses. They often explain why one room's flow rate checks out and the next one doesn't.
Balancing extraction/supply: step by step by zone to avoid drift
Work zone by zone. Start with the least favourable branch, then work back towards the shorter branches. Adjust the dampers, not the unit, as far as possible. After each correction, recheck 2 or 3 reference vents to avoid a domino effect.
Validating the results: tolerances, room-by-room consistency, and final speed setting
Aim for flow rates close to the design values, with a practical tolerance of around 10% per vent. Check the consistency between wet rooms and living rooms, then adjust the unit's speed last, to keep the overall balance stable. To frame these values, refer to the regulatory ventilation flow rates.
Airflow settings and air quality: optimising comfort and energy performance
Limiting over- and under-ventilation: impact on consumption, dry air, and odours
A correct flow rate setting avoids paying to over-ventilate. With over-ventilation, the unit extracts more heated air, increases fan consumption, and can give a dry-throat sensation. With under-ventilation, moisture and odours linger, with a risk of mould. Adjust the vents and dampers based on the sizing, measure with an anemometer, and check the filters and air inlets.
Optimising the bypass and the heat exchanger: summer/winter, defrosting, and condensate management
In winter, keep the bypass closed to make use of the heat exchanger and limit losses. Monitor the defrost mode (reduced flow rate, pre-heating) to avoid frost choking the exchange. In summer, open the bypass at night to cool down without reheating the fresh air. On condensate, plan for a slope, a trap, and accessible drainage. Otherwise, odours and leaks come back quickly.
Reducing noise: pitfalls to avoid on vents, ducts, silencers, and unit mounting
To aim for quiet operation, avoid vents that are closed too far and whistle, and crushed ducts. Limit tight bends, add a silencer near the unit, and favour acoustic ducts in sensitive rooms. Mount the unit on anti-vibration feet, with no rigid contact with the frame or partition walls. To go further, also consider the airtightness of mechanical ventilation ducts, which is often decisive for performance and nuisance.
Traceability and maintenance after commissioning: documents, client advice, and points to monitor
Formalising the commissioning: settings sheet, measured flow rates, photos, and labelling
After commissioning the ventilation system, leave the client a simple sheet. Note the settings, the flow rates measured at each vent, and the measurement method. Add 3 or 4 reference photos. Labelling of the unit, the main ducts, and the access points. The goal is clear traceability, with no arguments at a future maintenance visit.
Explaining maintenance: filters, access, frequency, and signs of clogging
Show where the filters are and how to open the hatches without damaging the seals. Give a realistic frequency. A visual check every 3 months, cleaning or replacement depending on how dirty they are. The warning signs are simple. Increasing noise, odours, condensation, a dropping flow rate. These are often signs of rapid clogging. To go further, you can point clients to mechanical ventilation maintenance.
Planning follow-up in 2026: check-up visit, seasonal adjustment, and routine troubleshooting
From 2026 onward, offer a check-up visit after a few weeks of operation. You check flow rates, the tightness of the connections, and condensate drainage if needed. Plan for a seasonal adjustment if use changes. For routine troubleshooting, start with the filters, the vents, and the electrical supply. That avoids 80% of callbacks, with no surprises.
Key figures
±10%
Supply/extract balancing
100-150 Pa
Network pressure
per the 1982 decree
Nominal flow rate
Frequently asked questions
Refer to the amended decree of 24 March 1982 (dwelling ventilation): as a baseline, you generally target 45 m³/h in the kitchen, 30 m³/h in the bathroom, and 15 m³/h in the WC (with possible peaks). Always validate against the manufacturer's manual and the network sizing, since pressure losses can require a different setting to reach these values at the vents.
Louis Meneteau
CPO of Argile
