Ventilation is the active process of “changing” or replacing air to regulate temperature and moisture. It should always occur under controlled conditions, by opening windows or with ceiling or exhaust fans, NOT through gaps and air-leakage.
Exhaust fans should always be self-closing, so that the replacement of air is controlled and not accidental. With out a self closing mechanism they are one of the main contributor of air leakage.
However, if they are self-closing they are an effective way to replace air, especially in rooms where no natural ventilation is available, or where natural ventilation might not be sufficient, such as kitchens or bathrooms.
Ceiling fans are an easy and cost effective way to improve the indoor air quality in summer and also to gain points towards the desired energy rating stars.
Ceiling fans provide additional air movement/wind, increasing the Relative Air Velocity (‘wind chill factor’) resulting in the apparent temperature felt on exposed skin to be 3 °C colder than the actual air temperature, thereby reducing the need for additional cooling.
Nowadays there are so many efficient fans available on the market.
If choosing a ceiling fan make sure you get one with at least 3 speeds, with the lowest speed being slow enough to still move air, but not to create a cool feeling draught, so that you can use them in winter mode)
Please note, if you are building a home according the the Passive House Guidelines, you won’t need exhaust fans in your wet areas anymore. The ventilation system will look after it. On the other hand, ceiling fans will also be really efficient and helpful in a Passive House.