Mechanical Ventilation with Heat Recovery (MVHR)

MVHR is a continuous mechanical ventilation system that simultaneously extracts stale indoor air and supplies fresh outdoor air while recovering heat from the extracted air to pre-warm incoming air. This process ensures energy-efficient ventilation with minimal heat loss.

Key Components

  1. Heat exchanger: Transfers ~90–95% of heat from outgoing air to incoming air.
  2. Dual fans: One fan extracts stale air; another supplies fresh air.
  3. Duct network: Distributes air between rooms and the central MVHR unit.
  4. Filters: Remove pollutants (e.g., pollen, dust) from incoming air.

How It Works

  • Extraction: Stale, humid air is removed from wet rooms (e.g., kitchens, bathrooms).
  • Supply: Fresh air is delivered to dry rooms (e.g., living rooms, bedrooms).
  • Heat recovery: The outgoing air stream warms the incoming air via the heat exchanger, reducing heating demand.
  • Energy savings: Typical UK retrofits report 20–30% reductions in space heating costs.

Practical Applications in UK Housing

Example 1: New Builds

  • Compliance: MVHR is increasingly specified in Passivhaus-certified homes to meet Part L (Conservation of Fuel and Power) Building Regulations.
  • Case study: A 2024 London development used MVHR to achieve an Air Tightness of <1.5 m³/(h·m²) while maintaining air quality.

Example 2: Retrofit Projects

  • Challenge: Older UK homes often lack airtightness, making MVHR installation complex.
  • Solution: Post-retrofit, a Victorian terrace in Manchester reduced its annual CO₂ emissions by 1.2 tonnes after pairing MVHR with insulation upgrades.

Advantages for UK Homes

  • Regulatory alignment: Supports compliance with Part F (Ventilation) and Future Homes Standard 2025.
  • Health benefits: Mitigates condensation and mould risks in airtight properties.
  • Cost efficiency: Payback periods of 5–8 years in energy bills are common.

Key Considerations

  • Installation: Requires professional design to balance airflow rates (typically 0.3–0.5 air changes per hour).
  • Maintenance: Filters need replacing every 6–12 months (cost: £30–£60).
  • Limitations: Less effective in poorly insulated homes; optimal performance requires airtightness <5 m³/(h·m²).