Ventilation -Mechanical

Overview

Ventilation is a major issue in the design of new homes. Modern houses are designed to be air-tight in order to reduce the heat loss caused by draughts. Following the maxim ‘build tight, ventilate right’, air for ventilation is provided in the winter by small trickle vents in the windows. Mechanical ventilation is sometimes used if a house is built to a very high standard of air-tightness. The traditional homes of Cheltenham are not air-tight; quite the opposite. They are often draughty and lose a lot of heat because warm air can so easily escape through all the gaps and cracks in the building fabric. This is why draught-proofing is such an effective way of in reducing heat loss in traditional homes. Nonetheless, even after draught-proofing, a Regency or Victorian home may have a higher rate of cold air infiltration than a home built to modern building standards.

Modern lifestyles create a lot of moisture indoors thanks to all our cooking, cleaning, clothes drying, showering and bathing. Despite the draughtiness of traditional homes, many people still actively ventilate rooms by opening windows or using extractor fans in order to reduce the risk of indoor condensation and mould.

Mechanical ventilation

Mechanical ventilation is usually only needed where water vapour or pollutants are produced, such as kitchens and bathrooms. In kitchens, extractors are often incorporated into cooker hoods and can be controlled manually so that they are only on when fumes are being produced. There should be a baffle in the hood to ensure that the there are no draughts when the extractor is not operational.

If you install an extractor fan in a bathroom, kitchen or utility room to remove water vapour, ensure that the fan is controlled by a humidistat, i.e. a sensor that is triggered when the humidity in the room gets too high. This ensures that the extractor does not run when it is not needed.

Heat-recovery ventilation (MHVR)

If you have been thorough in your draught-proofing and feel you need to improve the air quality in your home without pushing your energy losses back up again, you could consider installing a heat-recovery ventilation unit. This is positive pressure rather than extract ventilation. It sits within the wall or ceiling and provides a low level of background ventilation, transferring the heat from the outgoing air to the fresh air being drawn in. These systems run at a low power so the electricity consumption is less than the heat saved.