How Does Heat Recovery Ventilation Work

How Does Heat Recovery Ventilation Work

By Ruth MacEachern

Product Manager

With energy bills at record levels and the ongoing need to make our homes more sustainable, many homeowners are investigating ways to reduce their energy use and improve efficiency.  Minimising heat loss has been a major focus of home design in recent years, but increasing insulation and making a property almost airtight has the disadvantage of increasing humidity which can lead to condensation and problems with damp and mould. 

Good ventilation is essential in making our homes pleasant places, but this must be balanced against the need to maintain heat.

One way to prevent heat being lost from a home through ventilation is to use a system with a heat exchanger that captures the warmth of the outgoing air and uses it to heat up the air that is being drawn in to replace it.  This is known as Mechanical Ventilation with Heat Recovery or MVHR.

What is MVHR

Most homes will have extractor fans installed in wet rooms such as bathrooms and kitchens.  These extractor fans help to control humidity by removing moisture rich air and allowing it to be replaced with air that is drawn in from elsewhere in the property.  Extractor fans are an important part of any ventilation solution as they address the problem of humidity where it is most pronounced and as such help to stop condensation elsewhere in the building.

Modern extraction systems are designed to use as little energy as possible.  They feature highly efficient fan designs, low friction motors, and some, such as the EnviroVent Cyclone 8 have humidity sensors that adjust their power levels to remove moist air as quickly as possible, their use will still result in some warm air being lost to the exterior of the property.

MVHR adds an extra step into the air extraction process.  Rather than just being dispersed directly from the fan to the exterior of the building, the air drawn out of the property is passed through a heat exchanger.  The heat exchanger captures the warmth from the air and then uses it to warm air that is being drawn in from outside to replace the air that has been removed. 

How heat exchangers work

In its simplest form, a heat exchanger is a pipe within a pipe with fluids such as air moving in opposite directions.  Warm fluid is drawn in at one end and cold from the other.  As the two fluids pass each other, the colder fluid absorbs the heat from the warmer fluid.

In an MVHR system, the heat exchanger system features long thin coils of pipe to maximise the surface contact between the cool and warm air as it moves through the system.  The larger the contact area, the more heat can be retained.  In the case of an EnviroVent MVHR system, the heat exchanger is up to 85% efficient – it preserves more than 85% of the heat in the system.

Single room and whole house MVHR systems

MVHR systems are an increasingly popular choice for installation in new build homes.  Whole house MVHR systems work in a similar way to conventional Mechanical Extract Ventilation (MEV) system which extracts moisture laden air from throughout the property and exhausts it to the exterior of the property.  The MVHR system includes an intake for air which is drawn in through the heat exchanger.

In common with other MEV solutions, MVHR systems are typically only installed as part of either a full new build or a major renovation to a property.  It is possible though to achieve heat recovery in individual rooms using a single room MVHR system.

The HeatSava extractor fan is a single room MVHR system that can be used to replace a conventional extractor fan.  It can reduce the heat loss from kitchens and bathrooms and help to reduce energy bills for heating. 

Find out more

If you are concerned about condensation levels in your property and want to learn more about whether mechanical ventilation with heat recovery could help to improve your air quality while making your home more efficient, speak to our local experts.

EnviroVent have ventilation specialists across the UK who can visit your home to carry out a free ventilation survey.  They will identify the causes of condensation in your property and provide you with advice about the best solution for your needs.  Simply enter your postcode below to find an expert near you.