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MVHR Systems: A Complete Guide

Approx. 8 min read

Mechanical Ventilation with Heat Recovery (MVHR) systems are an advanced solution for ensuring continuous, balanced ventilation in modern, airtight buildings. By extracting stale, moisture-laden air and supplying filtered, tempered fresh air, MVHR units maintain healthy indoor air quality while recovering up to 95% of the heat that would otherwise be lost through traditional ventilation methods.

How MVHR Works

An MVHR system operates via two independent duct networks – one for extract air and one for supply air – connected to a central heat recovery unit.

  • Extract air is drawn from wet rooms such as kitchens, bathrooms and utility spaces.
  • Supply air is delivered to habitable rooms such as bedrooms, living rooms and offices.

Within the MVHR unit, a counterflow or crossflow heat exchanger transfers heat energy from the outgoing stale air to the incoming fresh air stream without mixing the two. High-efficiency heat exchangers can recover up to 95% of thermal energy, significantly reducing heating demand and improving energy efficiency ratings (SAP scores).

System Components

Typical components of an MVHR system include:

  • Central heat recovery unit – containing fans, filters, and the heat exchanger.
  • Ducting network – rigid or semi-rigid ducts that distribute air throughout the property.
  • Intake and exhaust terminals – external wall or roof terminals for air exchange.
  • Controls and sensors – variable speed fans, boost switches, humidity or CO₂ sensors.

Benefits of MVHR Systems

  • Energy efficiency – reduced heating costs and improved EPC/SAP scores.
  • Air quality – continuous supply of filtered, fresh air reduces pollutants and allergens.
  • Condensation control – removes excess humidity, preventing mould growth.
  • Thermal comfort – minimises cold draughts common with trickle vents or extract fans.
  • Acoustic improvement – sealed systems reduce outdoor noise ingress.

Design Considerations

MVHR performance depends heavily on design and commissioning. Key factors include:

  • Airtightness – MVHR is most effective in airtight dwellings (<3 m³/h·m² @ 50 Pa).
  • Ducting layout – smooth, balanced airflow with minimal pressure loss.
  • Heat exchanger efficiency – select a unit with tested efficiency (SAP Appendix Q listed).
  • Noise control – correct fan sizing and acoustic attenuation to meet Part F noise limits.
  • Maintenance access – filters must be accessible for cleaning and replacement.

Compliance and Standards

MVHR installations must comply with Building Regulations Part F (Ventilation) and Part L (Conservation of Fuel and Power). Systems should be designed and commissioned in accordance with:

  • BS EN 13141-7 (performance testing)
  • BS 5250 (condensation control)
  • Domestic Ventilation Compliance Guide

Correct commissioning and documentation are essential for Building Control approval and SAP assessment accuracy.

Is MVHR Right for Your Property?

MVHR is ideally suited to new builds and deep retrofit projects with high airtightness standards. In older, draughtier properties, energy recovery benefits may be limited, though localised solutions or hybrid systems can still offer improvements.

Flexivent Expertise

Flexivent provides professional design, supply, installation, and commissioning of MVHR systems throughout Gloucestershire and surrounding regions. Our engineers ensure systems meet current regulations, achieve optimal performance, and integrate seamlessly with your building design. Contact Flexivent for expert consultation on MVHR specification and compliance support.