Mechanical Ventilation with Heat Recovery (MVHR), also known as System 4, is a fan-based ventilation system with forced supply and extract, and heat exchange functions.

Mechanical Ventilation with Heat Recovery units save energy and reduce heating cost‎

The extract fan, supply fan, filters and heat exchanger are all part of the central MVHR unit, which can be located in cupboards, lofts and behind kitchen hoods. Plastic ductwork routes to rooms and is typically sited above ceilings with just the grilles on view, which complement the interior design.

These systems typically convey extract air from wet areas – such as kitchens, bathrooms, toilets and utility rooms – to the MVHR unit. The air is filtered and passed through a heat exchanger, which pre-warms incoming outside air before being exhausted to the outside.

The supply air fan draws air from the outside into the MVHR unit, where it is filtered and passes through the same heat exchanger to absorb heat from the extract air before being supplied to the habitable rooms, such as the living room and bedrooms.

In order for these systems to work efficiently, buildings need to be as air tight as possible with ideal maximum air leakage rates of 3m³/hr at 50Pa.



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