Balanced Ventilation

Save Energy

Improving air quality and saving money with mechanical ventilation systems with heat recovery


With the growing numbers of airtight, energy efficient homes in Bulgaria the issue of indoor air quality is becoming ever more important because natural ventilation by air infiltration has been significantly reduced. The process of air infiltration occurs when outdoor air leaks into a home through cracks or other openings due to pressure differences caused by wind or the buoyancy effect created by temperature differences or differences in humidity.

Ventilation is necessary to maintain a healthy and comfortable internal environment and to rapidly remove pollutants such as moisture, volatile organic compounds (VOC’s), allergens such as dust, oxides of nitrogen, carbon monoxide, carbon dioxide, tobacco smoke and unpleasant odours. Moisture is generally assumed to be the most significant of these pollutants because of the high rates of generation from cooking, bathing, washing, drying, breathing and the consequential condensation and mould growth problems.


However, when bringing outside fresh air inside a home, this fresh air has to be heated (or sometimes cooled) in order to maintain comfortable temperatures indoors. The energy load naturally varies according to the outside conditions, but it can often be more than 1kW, sometimes even 3kW. That could represent around half the overall heat load for some dwellings. To minimise the energy load, the inlet and outlet ducts around the house are connected to a heat exchanger that draws in the fresh air and pulls as much heat as possible out of the exhaust air. This system is known as a mechanical ventilation system with heat recovery (MVHR).

Mechanical ventilation with heat recovery means everyone in the home can have all the fresh air they require without having to pay the energy cost for heating it up to a comfortable temperature.

The air-to-air heat exchangers have been getting more and more efficient over the years and many achieve a heat recovery rate of over 50% at nominal conditions. Some claim to recapture as much as 94% of the heat from the exhaust air. Also the electric fans that drive them have been getting more efficient, thus further increasing the coefficient of performance of the ventilation system.

To select the most appropriate MVHR systems to work effectively, you are advised to contact a certified HVAC consultant to help you with determining the most suitable technical solution for your home by assessing its size, construction type and ventilation requirements and preparing designs that optimise the position of ducting, prevent noise from mechanical vibrations and internal turbulences and maximise the energy efficiency of the overall system.