Having adequate ventilation in our homes is important for our health: ventilation removes stale, damp air and replaces it with fresh air, helping to improve indoor air quality.

Although many people ventilate their home by opening windows and doors (known as ‘natural’ or ‘passive’ ventilation), people tend to do this less in winter due to the heat loss of opening a window when the heating is on.

Another common method is to use intermittent extractor fans in steamy rooms such as kitchens and bathrooms, Whilst reasonably effective, these fans usually aren’t left on for long enough to regulate indoor air quality in our homes.

Sometimes draughts are seen as providing sufficient ventilation to a home, but they are also a major source of heat loss and can make rooms feel uncomfortably chilly.

Modern energy efficient homes are more airtight (less draughty) than older buildings because they have to follow specifications for air-tightness, set out in the Building Regulations. Because of this, modern homes are sometimes fitted with Mechanical Ventilation with Heat Recovery (MVHR) systems.

These use heat exchangers to ensure heat isn’t lost due to air flowing inside and outside your home. A well-designed mechanical ventilation system provides clean, fresh air, reduces heat loss and improves energy efficiency.

How do mechanical ventilation with heating recovery systems work?

Whole-house MVHR systems extract warm, damp air from the home and draw in fresh air from the outside. The warm, extracted air is passed through a heat exchanger to recover the heat before being expelled outside. The cool, fresh outside air is also passed through the heat exchanger, without coming into direct contact with the pollutant air where it is pre-warmed before being pumped in to the property.

These systems tend to be made up of concealed ducting (piping) in ceiling cavities that lead to the heat exchanger unit in a cupboard, utility room or loft. Some units have an automatic or manual boost setting which can be used when generating excessive moisture, such as when cooking or washing. Air filtration is commonly built into MVHR systems to prevent pollen and other particles from entering the home, which provides a more comfortable environment for allergy sufferers and improves indoor air quality as the internal air contains fewer pollutants. Systems typically have between 80 – 90% heat recovery efficiency and are inaudible during normal use.

Decentralised MVHR systems are also available whereby multiple fans are installed on opposite sides of the property. These fans have individual heat exchangers and work together to provide cross-flow ventilation. These are cheaper to install than centralised MVHR system as they don’t require ducting.

What are the costs and savings of a MHVR system?

MVHR systems do require servicing as all equipment such as filters and fans must be kept clean to ensure effective operation. For decentralised MVHR systems, prices start from £600 per fan, for MVHR systems they start from around £3,000 but could cost well over £10,000, depending on the size and type of the system. It can be difficult to retrofit MVHR because of the space needed for ducting and the unit, as well as the challenge of achieving the level of airtightness needed for MVHR to work effectively.

Because the fresh air is pre-warmed, heat loss from ventilation is largely avoided. This means the householder can spend less on heating their property, reducing costs by around 25%, therefore saving money and ensuring a healthy, well-ventilated home.

Important things to note …

MVHR works best in buildings that are relatively airtight, such as new-build homes or older properties that are being fully refurbished.

Retrofitting MVHR needs to follow a comprehensive airtightness strategy, including a series of airtightness tests.