Understanding hygro-B mechanical ventilation and its value in renovation
Differences between self-regulating single-flow, hygro-A and hygro-B mechanical ventilation
Self-regulating single-flow mechanical ventilation extracts a near-constant flow rate, summer and winter alike. With hygro-A, the extract points open more or less depending on humidity, but the air inlets remain fixed. With hygro-B, both extract points and air inlets are humidity-controlled. The result: ventilation adapts better to actual use and limits heat loss when the home is dry.
How humidity-controlled regulation works on air inlets and extract points
Each extract point and air inlet includes a sensor (often a textile strip) that expands with humidity. When cooking or showering, the opening increases, and so does extraction. When the air becomes dry again, it closes back up. Regulation is passive, with no electronics, but it requires careful installation.
In which homes hygro-B mechanical ventilation really makes a difference (humidity, occupancy, airtightness)
It's relevant in renovation once insulation and airtightness have improved. It also helps in heavily occupied homes, or ones prone to condensation. In a very leaky house, the effect is limited. You need air inlets in dry rooms and well-sized extraction (see well-sized extraction).
Choosing hygro-B mechanical ventilation suited to your project
Flow rate, network, acoustics: the criteria that avoid callbacks
For hygro-B mechanical ventilation, check the stated regulatory flow rates and, above all, the available pressure. A network that's too long or too bent causes the actual flow rate to drop. Favour rigid or semi-rigid ducting, consistent diameters, and limit crushing. On the comfort side, check the noise level of the unit and extract points, and plan for acoustic sleeves if needed.
Compatibility with insulation and airtightness in high-performance renovation
With a reinforced envelope, ventilation becomes a safety component. Take care with penetrations using airtight sleeves, insulate ducting in cold zones, and keep suitable door undercuts. After installation, adjusting the flow rates and checking the air inlets prevents condensation and recurring odours.
Special cases: kitchen, multiple wet rooms, lofts, very airtight homes
In the kitchen, keep dedicated extraction and an extract point suited to humidity peaks. If there are several bathrooms, size the fan unit and connections to avoid imbalances. In lofts, suspend the unit and keep the filters accessible. In very airtight homes, carry out a measured commissioning, it's your safety net.
Installation and commissioning: the checks that secure performance
Positioning extract points and air inlets: avoiding short-circuiting and discomfort
For mechanical ventilation, fresh air must sweep through the home. Air inlets in living rooms, extract points in wet rooms. The aim is a good sweep of the volumes, without a draught over a bed or a sofa. Also check door undercuts to keep a continuous air path.
Networks: diameters, lengths, bends and airtightness to guarantee flow rates
Respect the planned diameters and limit lengths and bends. Every metre and every angle adds pressure losses, meaning noise or insufficient flow rates. Favour legible routing, well-fixed ducts, and careful connection airtightness (clamps, seals, suitable tapes) to avoid leaks.
Adjustments, measurements and checks: flow rates, pressure, noise and hygro-B operation
At commissioning, measure the flow rates at the extract points and check the pressure available at the fan unit. Adjust the settings to stay within the manufacturer's range. On the comfort side, check the noise level and vibrations. On hygro-B systems, test the opening of the extract points and air inlets according to humidity, then record the values for the project file.
Explaining hygro-B mechanical ventilation to the client and adding value to your quote
Concrete arguments: air quality, comfort, humidity, energy savings in renovation
Hygro-B mechanical ventilation adapts flow rates according to humidity. The air inlets and extract points are automatically controlled. You ventilate more when the bathroom or kitchen needs it, and less the rest of the time. The result: healthier air, less condensation, and a more consistent feeling of comfort. In renovation, it also avoids ventilation running "too strong" continuously, meaning less heat lost outside.
Maintenance and use: simple guidance to preserve the system's efficiency
Good habits keep performance going. Don't block the air inlets. Dust the extract points twice a year. Check that undercut doors still let air pass through. And plan a flow-rate check after installation, then periodically, to keep the right settings (and if needed, revisit the choice between self-regulating vs humidity-controlled mechanical ventilation depending on the home).
Quoting: line items to detail (unit, network, accessories, labour) and relevant options
- Unit, electrical supply, fixing and any anti-vibration mounts.
- Duct network, connections, insulation in cold spaces, roof or facade outlet.
- Hygro extract points and air inlets, sleeves, grilles, acoustic accessories.
- Commissioning, measurements, adjustments, labour and finishing.
Those four items fit into a single survey: the existing system, the room-by-room flow rates, the fan unit and the equipment go on the quote together.
