Construction defect · Defects & construction flaws
MVHR defects: noise, flow rate, balancing in new-builds
Severity Moderate
Reporting deadline 90 days
Warranty Two-year
Responsibility Installer
How to detect an MVHR defect?
A compliant MVHR (Mechanical Ventilation with Heat Recovery) must be silent in bedrooms (< 30 dB at night), deliver the regulated flow rates (Belgian EPC: 25 m³/h at bathroom, WC, kitchen extraction vents depending on volumes), be balanced between extraction and supply for double-flow models, with no annoying draft at the vents. Test: calibrated app sound level meter at supply vents in bedrooms, anemometer at extraction vents (kitchen, bathroom, WC), door-opening test (the MVHR should not slam the door due to excessive depression). Demand the commissioning report with measured flow rates vent by vent.
Before — compliant
silent MVHR 24 dB · flow 30 m³/h bathroom
Balanced · commissioning signed · silent in bedroom
⚠ After — defective
bedroom vent 38 dB · kitchen flow 12 m³/h
Noisy · low flow · adjust under warranty
Reporting procedure in 4 steps
A misadjusted MVHR is reported like any equipment. The two-year warranty covers equipment, the ten-year liability covers consequences (damp, mould).
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1
Measure flow and noise
Digital anemometer at extraction vents (air speed x section). Calibrated app sound level meter 1 m from supply vents. Note time (day/night) and mode (boost or normal).
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2
Demand commissioning report
The MVHR commissioning report must include measured flow vent by vent, static pressure, balancing. Without this document, EPC compliance is challengeable.
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3
Formal notice
Registered letter to the installer and contractor within 90 days. Attach measurements, commissioning report (or its absence), regional EPC references (W, B, F).
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4
Ventilation expert assessment
Independent thermal engineer with ventilation kit (anemometer, sound meter, balometer). Admissible report · from €380 VAT incl.
Who pays for the adjustment? Responsibility table
The ventilation installer is responsible. The main contractor is jointly liable for the EPC calculation.
Noisy MVHR in bedroom
✓ two-year warranty
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Low flow bathroom/WC/kitchen
✓ two-year warranty
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Faulty balancing
✓ two-year warranty
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Condensation from low flow
✓ ten-year liability
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Clogged filters (post-1 year)
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✓ maintenance
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Get an inspection
Independent ventilation diagnosis
Flow and noise measurements · admissible report · €380 VAT incl.
FAQ
Common questions about MVHR
My MVHR whistles in a bedroom. What should I do?+
Often a badly adjusted vent (excessive flow) or a pinched/crushed duct. Covered by the two-year warranty. Demand adjustment and duct inspection. If duct damaged, heavier intervention (suspended ceiling).
What is the minimum flow for my bathroom?+
Under regional EPC: minimum 25 m³/h at nominal flow, 50 m³/h in boost mode. If you measure less than 20 m³/h at nominal, reportable defect. Digital anemometer essential for the measurement.
My double-flow MVHR is noisier than expected. Normal?+
Noise level at the unit must be < 35 dB (boiler/utility room), at bedroom supply vents < 25 dB at night. Beyond: acoustic absorption defect or poorly insulated unit. Two-year warranty.
I am missing the MVHR commissioning report. Important?+
Very important — request by registered letter. This document certifies EPC compliance and triggers the warranty. Without commissioning, you can demand the free check or obtain one at recoverable cost.
How much does a full ventilation diagnosis cost?+
Between €380 and €550 VAT incl. Includes: flow measurements vent by vent with anemometer, sound level, double-flow balancing check, duct tightness test. Recoverable if defect confirmed.