Understanding the role of the air inlet in a hygro B mechanical ventilation system
Hygro B mechanical ventilation: basic principle and difference from hygro A
A humidity-controlled mechanical ventilation system adapts airflow to the home's humidity level. In hygro A, extraction is modulated in wet rooms, but air inlets in living spaces generally remain fixed. In hygro B, both extraction and air inlets are humidity-controlled. This produces more coherent variable flow rates depending on occupancy, cooking or showers.
Why the humidity-controlled air inlet complements extraction (flow-rate balancing)
The extractor fan creates negative pressure. Without a suitable air inlet, air looks for other paths: leaks, shutter housings, hatches. A humidity-controlled air inlet opens just enough to feed air transfer toward the kitchen, bathroom and toilets. The result: controlled pressure, less whistling and more stable ventilation.
On-site signs of a poorly matched air inlet: condensation, odors, discomfort
On site, an air inlet that's too weak, blocked or poorly installed shows up quickly. Typical symptoms: persistent condensation on windows, lingering odors, a localized sensation of cold air, slamming doors, suction noise, mould in corners despite correct extraction. To go further on sizing air inlets and extract vents, see air inlets and extract vents.
Choosing the right humidity-controlled air inlet for the home and the ventilation system
Choosing the right type: window frame, transom, or roller-shutter housing (depending on the job)
On a renovation, start from the substrate. On new windows, the air inlet is often installed in the rebate or in an upper transom. On a replacement without changing the window, an add-on transom avoids weakening the frame. With a roller shutter, a housing-mounted model limits finish touch-ups. Aim for a clean installation that's accessible for maintenance.
Flow rates, acoustics and compatibility: what to check on the product data sheet
The data sheet must specify the nominal flow rate and the humidity-controlled range, as well as the acoustic rating (sound reduction). Also check compatibility with your ventilation system (self-regulating, hygro A, or hygro B) and the type of slot, thickness and accessories. A poorly sized air inlet unbalances the ventilation and increases discomfort.
Special cases: wet rooms, bedrooms, older homes and windy areas
As a general rule, place the air inlet in the main living rooms, not in wet rooms where extraction does the work. In bedrooms, favour quieter models. In older buildings, check window airtightness and parasitic infiltration. In windy areas, choose anti-draught options to maintain a stable flow.
Installation and airtightness: fitting an air inlet cleanly, without degrading insulation
Location and drilling: best practices for an effective, discreet air inlet
Choose a location consistent with the planned ventilation system. In renovation, the air inlet is most often placed in the upper part of the window frame, or in an exterior wall if the manufacturer allows it. Drill to the template, without "enlarging by hand." Locate reinforcements, cables and networks beforehand. A clean cut means less noise, less dust and a more durable installation.
Airtightness treatment: avoiding parasitic leaks around the air inlet
The key point is continuity of the air barrier. Install the sleeve or frame provided, then treat the perimeter with a suitable seal (sealant, sealing tape, compression tape depending on the substrate). Foam alone doesn't provide reliable airtightness. Aim for continuous contact, with no gaps.
Common job-site mistakes: blockage, poor cutting, thermal bridges
Classic issues: grilles blocked by paint or dust, an air inlet hidden behind a curtain, an oversized cut that "floats," no thermal break at a wall penetration, or a poorly sealed insulation patch that creates a small thermal bridge. Check the flow rate, then run a simple smoke test to spot a leak right away. To go further on causes and solutions, see a small thermal bridge.
Settings, checks and commissioning: validating proper operation with the ventilation system
Adjusting the vents and checking the airflow path (air inlet → wet rooms)
Start by checking that the air inlets in dry rooms are clear. The air inlet must be able to flow through the home toward the kitchen, bathroom and toilets. Check door undercuts and the absence of obstacles in the ducts. Adjust each vent according to the flow rate specified in the manual. A well-balanced ventilation system limits humidity without over-ventilating.
Simple checks to run with the client: tests, noise, draw and sensation of cold
With the client, run simple tests. A sheet of paper should be held in place by suction on an extract vent. Listen to the sound level at low and high speed, especially at night. To go further, also see solutions for reducing mechanical ventilation noise. Check there's no odor backflow, and that the sensation of cold isn't coming from a poorly oriented air inlet or an excessive flow rate.
Maintenance: cleaning, replacement and points to monitor after a few months
Schedule a visit after a few months. Clean the vents and air inlets, dust the unit. On a heat-recovery system, change the filters according to the manufacturer's recommended frequency. Monitor vibrations, condensate, duct fouling and changes in humidity.
Compliance and grants in 2026: securing your ventilation job and your supporting documents
Certification and useful documents: what you need to record to avoid callbacks
Record everything. Keep the signed quote, the detailed invoice (brand, references, flow rates, accessories), the technical data sheet, and a commissioning report. Add 3 simple photos (before, during, after) of the unit, vents and penetrations. This is often what prevents a file from being sent back.
2026 funding: when the air inlet is covered and how to explain it
For the funding schemes, ventilation is justified as a coherent trade package. On an extract-only mechanical ventilation system, the air inlet is part of the balance. Note its presence, its type (self-regulating or humidity-controlled) and its location. In the scheme's paperwork, stick to the facts. What matters is traceability.
Coordination with the energy audit: consistency between ventilation, insulation and heating
After insulation work and a heating-system change, air needs evolve. Revisit the audit's recommendations. Show that the ventilation system, the air inlets and the settings follow the chosen scenario. Clear consistency limits requests for additional documents and reassures the client. It is also what makes the pricing hold up: the existing system is surveyed and flow rates set room by room, air inlets included.
