Heat Recovery Ventilation Systems

Mechanical ventilation with heat recovery saves energy in the home by extracting the heat from the waste air before it leaves the building and using that heat to warm the incoming fresh air. The MVHR system can also be used in reverse to conserve “cool” in the summer by cooling incoming air using the cool outgoing air.

The system contains a heat exchanger with fans to regulate air movement, filters and ducts to distribute the fresh warmed air throughout the house.

A house loses heat though its fabric and through ventilation. A typical existing house in the UK loses about 20% of its heat though uncontrolled ventilation (draughts). For a refurbishment with high insulation levels, if thought is not given to improving air tightness, the heat loss through ventilation can be around 35% of the total.

Building Requirements

For MVHR to be a worthwhile investment, air flow must be through the MVHR unit rather than through uncontrolled draughts. For retrofits, as an achievable target is 3m3/hr/m2.

A decision on whether to install MVHR needs to be taken as early as possible in the design to ensure air-tight design details and enable the ducting and installation of the system to be carried out in an air tight manner.

Air Tightness Standards

m3/hr/m2 @50pa
The Building Regulations 2006 10
EST 'Good practice' 5
EST 'Best practice' 3
The AECB Gold Standard 0.75

System Design

Good design of the MVHR system is important for a number of reasons:

  • To increase longevity
  • To ensure quiet operation
  • To ensure low running costs through efficient duct positioning and sizing
  • To ensure efficient running at below-zero temperatures