The order of 24 March 1982 nowhere compares self-regulating and humidity-controlled ventilation. It sets floors, and it sets two of them. Without automatic modulation, the total extract rate never drops below 35 m³/h in a one-room dwelling and 135 m³/h in a seven-room one. With a modulating system approved by the ministers responsible for construction and for health, that same floor falls to 10 m³/h and 35 m³/h respectively, roughly a quarter of the permanent regime. The whole economic case for humidity control sits in that gap, and nowhere else.
Understanding single-flow mechanical ventilation: what you're actually installing
Principle of single-flow mechanical ventilation and key points on site
Single-flow mechanical ventilation puts the home under slight negative pressure. The fan unit extracts air from wet rooms (kitchen, bathroom, WC), and fresh air enters through air inlets in dry rooms. On site, aim for careful airtightness of the ductwork, reasonable duct lengths, and a transfer air path matching the system's technical approval so that sweeping actually happens. To go further on this point, also see mechanical ventilation duct airtightness.
Self-regulating vs humidity-controlled: clear definitions and quick reference points
With self-regulating systems, flow rates stay close to a fixed value, reproducible from one job to the next. With humidity-controlled systems, extract points and sometimes air inlets open according to humidity. The BAR-TH-127 sheet settles the vocabulary: a system is type A if only the extract points are humidity-controlled, type B if both the extract points and the air inlets are. That distinction is not marketing, it drives the certificate value and the nature of the supporting evidence.
The two flow-rate tables the order of 24 March 1982 imposes
Article 4 sets the permanent regime, article 3 the peak regime. A compliant system has to hold both, whatever its control principle.
| Number of main rooms | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| Minimum total extract rate, 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, article 4 (m³/h) | 10 | 10 | 15 | 20 | 25 | 30 | 35 |
The peak rate, by contrast, does not modulate: it has to stay reachable at all times.
| 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 |
Extract points, air inlets, fan unit: the elements that make the difference
Performance comes down to the details. Extract points suited to each room, unobstructed air inlets, and a fan unit sized to the ductwork limit noise and under-flow rates. Plan for access, cleaning, and flow-rate checks. Ventilation is judged on the commissioning record, not on the box.
Comparing self-regulating and humidity-controlled single-flow ventilation: performance and comfort
How far humidity-controlled systems are allowed to drop
This is the only question that genuinely separates the two families. Article 4 reserves the lowered floor for devices that "allow automatic modulation of flow rates", and it states that such devices must be approved by the ministers responsible for construction and for health, each setting its own minimum threshold. In practice the CCFAT technical approval is what embodies that authorisation, and BAR-TH-127 makes it a condition for issuing certificates. A component outside its technical approval, or a mix of incompatible ranges, takes you out of the derogation: you fall back onto the full 35 to 135 m³/h floor, and the saving promised to the client disappears. In a block of flats that floor is also what sets the cumulative flow of an extract riser, and therefore its diameter.
Acoustic comfort and air quality: criteria to check room by room
The order of 30 June 1999 gives the benchmark to produce if a complaint arrives: the normalised sound pressure level from an individual item of building equipment must not exceed 30 dB(A) in main rooms and 35 dB(A) in the kitchen, with individual ventilation running at minimum flow. So check the noise at the permanent regime, the one that runs continuously, not only at peak. On filtration, check the air inlets if the site is exposed to dust or pollen.
Electricity consumption and heat losses: concrete impacts in renovation
On the electricity side, the difference comes from the motor and the time spent at high flow. BAR-TH-127 caps the unit's weighted absorbed power at 15 WThC in a four-room configuration for a single-dwelling installation, and requires energy efficiency class B or better. On the thermal side, humidity control lowers the average flow rate and therefore the heat losses carried by extracted air. Without minimum airtightness, parasitic air cancels part of the gain.
Choosing correctly based on the home: your decision method (house, apartment, wet rooms)
Older home, airtightness, insulation: adapting ventilation to the renovation level
In leaky fabric, ventilation that is too strong increases parasitic inlets without improving sweeping. When you rework insulation, also check airtightness and the building's ability to dry out. Without whole-home renovation, a type A humidity-controlled single-flow system is usually the best risk-to-result ratio. After a full envelope rework, heat-recovery ventilation becomes defensible if the ducts stay short and accessible.
Kitchen, bathroom, WC: sizing and positioning to hold the article 3 rates
These rooms concentrate steam and odours. Place extract points near the sources, avoid burying them behind units, and keep air inlets in dry rooms to ensure proper sweeping. Sizing follows the table row matching the number of main rooms, not an average catalogue figure.
Special cases: lofts, long duct runs, multi-unit building constraints
In lofts, insulate the ducting, limit lengths, and plan easy access for maintenance. With long runs, reduce bends and check pressure losses, otherwise the kitchen peak becomes unreachable. In a co-owned building, anticipate votes, facade or roof outlets, and compatibility with existing service shafts.
Installation and adjustment: avoiding mistakes that ruin good single-flow ventilation
Ductwork, diameters, lengths, connections: limiting pressure losses and noise
For ventilation that holds its flow rates, take care with the ductwork. Keep runs as short as possible, with few bends and clean connections. Respect the diameters set by the technical approval, seal every joint, and avoid crushing. A regular route, with a wide radius, limits noise.
Flow-rate adjustment and on-site checks: verifications to carry out systematically
After installation, don't leave without a record. Adjust the extract points one by one, then measure the flow rates with an anemometer or a cone. To go further on methods and instruments, see measuring flow rates. Also check the balancing between wet rooms, the direction of rotation, and the absence of leaks at the unit. The goal is a measured flow rate that is stable, recorded and defensible.
Maintenance and access: filters, extract points, cleaning and after-sales points
Plan for easy access to the unit, the extract points and the air inlets. Schedule regular dusting of the extract points and periodic cleaning of the fan unit. Note the references, file the instructions and the technical approval, and secure easy access for after-sales work.
Quoting and client arguments in 2026: defending your choice against a cheaper bid
Quoting: equipment, accessories, labour and useful options
On the quote, present the ventilation system item by item. The vague lump sum is exactly what loses you the job against a cheaper competitor, because it makes both offers comparable on price alone. Separate equipment, accessories, labour, then finishing, which a quote built from the lines of the works plan produces without re-keying.
- Equipment. Ventilation unit, extract points, air inlets, ducting, any silencers, with brand and reference.
- Labour. Drilling, installation, connections, adjustments, flow measurement and handover report.
- Useful options. Maintenance access, casing, acoustic treatment, rework of existing ductwork.
The argument that holds: produce a table, not a promise
Faced with a cheaper bid, don't argue about the brand, argue about the flow rate. A quote offering humidity-controlled ventilation without stating type A or B, without a CCFAT technical approval and without a commitment to measure at handover gives no way to verify the article 4 derogation. Yours does, and that is what puts your own liability insurance behind the job rather than nobody's.
To coordinate with the rest of the energy renovation package: insulation, windows, heating
In 2026, homes become more airtight after insulation and window replacement, and ventilation becomes the item that absorbs the difference. Coordinate air inlets with the windows, plan duct routing before wall linings go up, and check compatibility with the heating system, especially where a room-sealed combustion appliance is involved. These three checks belong to the same survey: the system in place and its sub-type, the air inlets to create in the dry rooms and the combustion safety checks.
