A humidity-controlled extract vent is chosen on two regulatory figures, not on a catalogue modulation range. Article 3 of the order of 24 March 1982 sets the peak rate the room must be able to reach at any time, from 75 to 135 m³/h in the kitchen depending on the number of main rooms. Article 4 sets the permanent floor, and it allows an approved automatically modulating system to take the dwelling's total down to 10 m³/h in a one-room dwelling and 35 m³/h in a seven-room one, against 35 to 135 m³/h without modulation. The BAR-TH-127 sheet adds the condition that locks it all together: a valid CCFAT technical approval, without which neither the derogation nor the certificate value holds.
Understanding the role of a humidity-controlled vent in a ventilation system
Extract vent: what it actually has to deliver on site
The extract vent draws stale air out of wet rooms, bathroom, WC, kitchen, and sends it to the fan unit and then outside. It is not a finishing accessory: it is the component at which the flow rate is measured at handover, so it is what decides whether the installation is compliant. Everything else in the ductwork exists only to let it hold its figure.
Humidity-controlled: how airflow adapts to humidity without manual adjustment
A humidity-controlled vent varies the airflow rate automatically with ambient humidity. When vapour rises, the opening widens. When the air dries out again, it partially closes. The point is not the convenience of automatic setting, it is regulatory: that behaviour, once approved, is what unlocks the lowered flow floor of article 4.
Single-flow ventilation: where the vent sits and how it works with air inlets
On a single-flow system, the vent is fitted in the ceiling or high on a wall in wet rooms, connected by ducts to the fan. Fresh air enters through the air inlets in living rooms, then flows towards the wet rooms through the transfer paths. That air path makes the whole dwelling work as one circuit, under slight negative pressure. If the transfer path is blocked, the best vent on the market will not hold its flow rate.
Built-in humidity sensor: what to check before choosing a vent
Airflow range, humidity range and responsiveness: the points to compare
Start with the advertised airflow range, then set it against the peak rate required for the room, not against an average. Then compare the humidity range the vent responds to and its responsiveness, especially after a shower or while drying laundry. Those figures do not have to be hunted down datasheet by datasheet at pricing time: Argile keeps a catalogue where the technical data of the fitted reference are verified and up to date.
- Minimum and maximum airflow advertised, under the test conditions stated in the technical approval.
- Opening thresholds and whether adjustment or a delay function is available.
- Return to base airflow, noise at the permanent regime, and sensor maintenance.
Compatibility with your ductwork: diameter, connection, pressure losses
Check the diameter and the type of duct connection. In dwellings, common ducts run in 80 mm or 125 mm depending on the room. Also check the stated pressure loss: if it is high, your fan unit will lose airflow on that branch, and the kitchen shows it first, because that is where the required peak is highest. To go further, see also sizing the ventilation ductwork.
The flow rates to hold room by room, and the floor allowed with modulation
The first table is the one you size against, room by room. It gives the peak rate, which must stay reachable at all times, whatever the vent technology.
| Number of main rooms | Kitchen | Bathroom | Other shower room | WC |
|---|---|---|---|---|
| 1 | 75 | 15 | 15 | 15 |
| 2 | 90 | 15 | 15 | 15 |
| 3 | 105 | 30 | 15 | 15 |
| 4 | 120 | 30 | 15 | 30 |
| 5 and above | 135 | 30 | 15 | 30 |
The second is the one that justifies humidity control. It gives the dwelling's permanent total flow, without modulation and then with approved automatic modulation.
| Number of main rooms | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| Minimum total flow, article 4 (m³/h) | 35 | 60 | 75 | 90 | 105 | 120 | 135 |
| of which kitchen, article 4 (m³/h) | 20 | 30 | 45 | 45 | 45 | 45 | 45 |
| Reduced total with automatic modulation (m³/h) | 10 | 10 | 15 | 20 | 25 | 30 | 35 |
In practice this drives the room-by-room choice. In the kitchen, a dedicated vent with high available flow, ideally with a boost control, because the humidity sensor responds to vapour but not to cooking odours. In the bathroom, a humidity-controlled vent with a fast rise and a gradual return. In the WC, a low-flow but responsive model is enough, except in a dwelling of four main rooms or more with several WCs, where the peak rises to 30 m³/h.
Installation and site adjustments: getting a humidity-controlled vent right
Positioning, sealing and fixing: avoiding parasitic air leaks
Fit the vent in the right room and in the right spot, as close as possible to the wet zone. Take care over the vent-to-support connection with a continuous seal and stable fixing. No play, no gap. Otherwise parasitic air leaks distort the measured flow rates and increase noise, and you end up hunting a fan unit fault that does not exist.
Airflow adjustment and end-of-job checks: a simple, quick method
On a humidity-controlled unit, the vent modulates itself. What you verify is the base flow rate against the technical approval, and the ductwork's ability to reach the article 3 peak. Quick check: cover properly clipped on, no obstruction, then measure with a flow meter or anemometer at each connection. Record your readings room by room. This is your end-of-job airflow check, and the only item in the file worth anything if the job is disputed.
Common mistakes: mounting direction, duct length, early clogging
The classics: vent fitted upside down, duct too long or crushed, tight bends that choke the ductwork. Protect the vent during dusty work and clean it before commissioning. Otherwise you end up with early clogging, an unreachable kitchen peak and complaints within six months.
Maintenance and troubleshooting: keeping a vent effective over time
Periodic cleaning: what to do without damaging the humidity sensor
A humidity-controlled vent should be cleaned gently, at the interval stated by the manufacturer. Cut the ventilation system's power, unclip the cover and dust it with a brush or vacuum, soft brush attachment. Wipe the grille with a slightly damp cloth. Avoid sprays, running water and any soaking. The humidity sensor must stay dry. Let it air-dry before reassembling.
Airflow too low or too high: diagnosing between vent, duct and fan unit
If the airflow drops, start with the vent (clogging, stuck damper). Then check the duct (crushed, punctured, disconnected), then the fan unit (fouled, filter to clean depending on model, fan wheel labouring). If airflow is too high, check that the vent is fitted in the correct room, that the ring is in place, and that nothing has been altered on the unit's settings. A bathroom vent fitted in a WC is enough to take both rooms outside the article 3 values.
Noise and whistling: common causes and on-site fixes
Whistling often comes from a clogged grille or an air leak around the vent. Clean it, reposition it, add a foam seal if needed. Vibrations point more towards the fan unit or a duct touching the roof structure. Tighten the fixings, decouple with a short flexible duct section and fit anti-vibration pads. The target to hold is the one in the order of 30 June 1999, 30 dB(A) in main rooms and 35 dB(A) in the kitchen. To go further on noise issues, see also attenuation solutions.
In 2026: selling the right vent with the right ventilation system (comfort, humidity, savings)
What you write for the client, and what actually binds you
An air-quality argument does not stand on its own against a cheaper bid. What does stand is a flow-rate commitment: the required peak per room, the permanent floor, and the measurement at handover. A vent suited to the room and its use clears vapour better, but it is the recorded figure that engages your liability, not the comfort promise.
Energy retrofit: consistency with insulation, airtightness and ventilation
After insulation and airtightness work, humidity stays indoors unless ventilation is brought up to standard in the same job. That is where a system consistent with its vents makes the difference: humidity-controlled under technical approval to benefit from the lowered floor, or heat-recovery ventilation if the project allows. The goal remains flow rates that hold without over-ventilating, which means dealing with air inlets and transfer paths as well. All three are surveyed room by room: kitchen, bathroom and WC documented with the vent each one receives, and the air inlets to create in the dry rooms.
A clear quote: specify the vent, the system, the flow rates and the rooms concerned
Be precise on the quote. Vent type (kitchen, bathroom, WC extract), technology and type A or B, diameter, accessories, and the associated system with its technical approval reference. State the rooms concerned and the target flow rate per room, as well as balancing and commissioning. A line-by-line quote makes your offer comparable on something other than price, which is exactly what a vague quote prevents. That level of detail comes straight out of the costing: Argile builds the quote from the equipment and works selected, with VAT applied line by line.
