In the kitchen, where the fan is fitted to the outside wall or window panel, an Axial Fan would be the most suitable. Between 15 to 20 air changes per hour are considered necessary. The lower figure applies when the air temperature is warm and cooking times short, the higher figure when the kitchen is cool and steam and cooking fumes are troublesome.
Ideally, a two speed fan gives greater control, the higher setting provides the maximum air changes required (as calculated) and the lower where the conditions are more favorable or when working in conjunction with a cooker hood extractor.
One air change is equivalent to the volume of the room, so to help select the right extractor fan, calculate the volume of the room, (length x height x width, in metres) multiply this by between ten or twenty, as in the case of the kitchen. Purchase a fan that is the closest match to your resulting figure. If you find that your particular requirement falls between two fans, its better to go for the more powerful model rather than less (within reason that is).
The Dreaded Kitchen
The kitchen has an added problem of moisture particles that carry grease, which can settle anywhere that the air reaches, creating a potential breeding ground for germs. For this reason, the kitchen would further benefit from a cooker hood with a built-in extraction unit and removable filter, ideally situated over the hob where the cooking takes place. Very often though, the hoods are not connected to any ducting system, resulting in the fan drawing air through the filter only. The built in valve, which can be manually opened if a ducting is fitted, is set to the 'closed' position resulting in the filtered air re-circulating into the room.
Ducting components can be purchased for connecting onto this valve, which, when opened, will allow air from below to be first drawn through the filter, then into the ducting tube that will carry the unwanted air to the nearest outside wall or roof vent, where it can escape.
It goes without saying that this is a must in the kitchen and is especially effective when working in conjunction with the main kitchen extractor fan, as it goes a long way in controlling condensation by removing moisture and smells from source as well as filtering grease particles in the process.
Extractor Fans in the Bathroom
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