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
- Heat exchanger: Transfers ~90–95% of heat from outgoing air to incoming air.
- Dual fans: One fan extracts stale air; another supplies fresh air.
- Duct network: Distributes air between rooms and the central MVHR unit.
- 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).