What Is MVHR? — Mechanical Ventilation with Heat Recovery

Definition

MVHR (Mechanical Ventilation with Heat Recovery) is a whole-house ventilation system that provides continuous fresh air while recovering heat from the extracted stale air. The system uses a counter-flow or cross-flow heat exchanger to transfer heat from the outgoing exhaust air to the incoming supply air, typically recovering 85-95% of the heat energy. MVHR is the preferred ventilation strategy for highly insulated, airtight buildings and is increasingly common in new-build UK homes.

When Is It Used?

MVHR is used in new-build homes designed to high airtightness standards (typically below 3 m³/(h·m²) at 50 Pa), Passivhaus projects, and some retrofit projects. It is one of four ventilation strategies recognised by Part F of the Building Regulations (System 4). MVHR is particularly beneficial where trickle vents and extract fans alone cannot provide adequate ventilation without excessive heat loss, and in urban environments where opening windows is undesirable due to noise or air quality.

Key Facts

• Heat recovery efficiency: typically 85-95% (SAP Appendix Q listed units)
• Specific Fan Power (SFP) should be below 0.7 W/(l/s) for Part L compliance
• Ductwork should be rigid metal (galvanised steel or aluminium) for best performance
• Supply air to bedrooms and living rooms; extract from kitchen, bathroom, utility, and WC
• Part F minimum whole-dwelling ventilation rate: typically 13-29 l/s depending on number of bedrooms
• Summer bypass mode allows cool night air to enter without passing through the heat exchanger
• Filters must be cleaned or replaced every 3-6 months
• Typical electricity consumption: 30-60 kWh per year (less than a fridge)

Related Calculators

Use the Ventilation Rate Calculator for Part F airflow requirements, or the Heat Loss Calculator to see the impact of heat recovery on heating demand. See also the Airtightness glossary entry.