Mechanical ventilation with heat recovery
New houses are rather airtight. Or at least, they are compared to older, draughty ones. As a result, they are required to have some form of ventilation; the standard way of doing this is to fit extractor fans in the kitchen and bathrooms and to have small slots cut into the heads of the windows to let air in. These slots, known as trickle vents, are a peculiarly British way of building, and are renowned for not being particularly effective. When the wind is blowing in the right direction, they can work well, but when there is no wind, they do little beyond leaking heat. What’s more, given that
