What is MEV?
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- What is MEV?
MEV is a type of ventilation system that extracts stale air from wet rooms (kitchen, bathroom, utility) and lets fresh air enter naturally through vents in living areas (bedrooms, living rooms). Unlike a full MVHR (Mechanical Ventilation with Heat Recovery), MEV does not supply air mechanically — it only removes it.
How does MEV work?
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Air Extraction
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The system has a central fan (usually one fan in the loft or utility) that draws air out of wet rooms. – Click here to see our new C4A MEV fan
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Path of Air
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Extracted air moves through ductwork connected to the fan.
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The ducts are typically rigid or semi-rigid and sized to maintain correct airflow rates.
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Entry of Fresh Air
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As stale air is removed, fresh air enters naturally through:
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Background vents in bedrooms and living rooms
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Trickle vents in windows
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Other designed air inlets
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This creates a slight negative pressure, pulling air through the house from clean to wet areas.
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Filtration
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Most MEV units have a filter at the fan inlet to stop dust and insects entering the system.
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Filters need regular cleaning or replacement.
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Control & Commissioning
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Proper MEV systems require balancing to ensure each room gets the right airflow.
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Too high flow → noise, drafts, energy waste.
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Too low flow → poor humidity control, condensation, and mold risk.
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Pros and Cons of MEV
Pros:
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Simpler and cheaper than MVHR.
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Flexible installation in existing homes.
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Less maintenance than systems with supply fans.
Cons:
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No heat recovery → can increase heating demand.
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Relies on good natural air inlets.
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Less precise airflow control if not commissioned correctly.
MEV is all about removing stale air efficiently and letting fresh air come in naturally. The system only works properly if ducts are correctly sized, terminals are right, and it’s commissioned to balance airflow across the home.
MEV DIAGRAM
Written by – Sean Roche
To meet the demands of today’s energy-efficient homes, Aereco introduces the new C4A MEV Whole House Fan.
Designed to combine performance, discretion and ultra-low energy consumption, the C4A delivers continuous, reliable ventilation while helping to reduce running costs. Compact and lightweight, it is suitable for wall, ceiling or floor installation, offering maximum flexibility on site.
