MEV is a ventilation system that operates 24/7 to remove stale, humid, or polluted air from specific areas of a building, particularly “wet rooms” (e.g., bathrooms, kitchens, utility rooms). Unlike intermittent extract fans, MEV systems run continuously at a low background rate and can boost extraction during high-moisture activities (e.g., showering).
Key Features
- Continuous Operation: Extracts air at a low rate (e.g., 8–13 l/s for bathrooms/kitchens) and switches to a higher rate when needed.
- Ducted Network: Typically uses ducts to channel extracted air to a central fan unit, which discharges it outside.
- Background Ventilators: Requires passive air inlets (e.g., trickle vents) in habitable rooms (e.g., bedrooms, living rooms) to allow fresh air infiltration.
- Compliance: Must meet minimum airflow rates specified in Approved Document F (Table 1.2), e.g., 13 l/s for kitchens and 8 l/s for bathrooms.
Practical Applications
- New Builds: Installed in airtight, energy-efficient homes where natural ventilation is insufficient.
- Retrofits: Used to upgrade older properties during renovations (e.g., replacing single-point extract fans) to comply with Part F.
- Wet Rooms: Ideal for kitchens with cooker hoods or bathrooms with showers, where moisture control is critical.
Example: In a 1930s terraced house retrofitted with insulation and draught-proofing, MEV ensures moisture and pollutants are consistently extracted, preventing mould and maintaining indoor air quality.
Relevance to UK Building/Retrofit
- Part F Compliance: MEV is a common solution for meeting ventilation requirements in dwellings with airtightness ≤5 m³/(h·m²) at 50Pa.
- Retrofit Challenges: Older homes often lack adequate ventilation; MEV systems are easier to install than full Mechanical Ventilation with Heat Recovery (MVHR) and avoid reliance on occupant-operated windows.
- Energy Efficiency: Works alongside insulation upgrades by balancing airtightness with controlled airflow, reducing heat loss compared to uncontrolled infiltration.
Installation & Maintenance
- Commissioning: Requires airflow testing (per Approved Document F, Section 4) to verify rates match design specifications.
- Maintenance: Filters (if fitted) and ductwork must be cleaned regularly to prevent blockages.
- Noise Control: Designed to operate quietly (≤30 dB in bedrooms, ≤45 dB in kitchens).