Choosing the correct size of fan
The size, or
capacity, of the fan should be determined by the type of room it is to be installed in, as
different rooms require different rates of air flow. Typically one considers the rate of air flow as the number of complete changes of air within the room per hour;
- Kitchen – 10-15 times per hour
- Bathroom – 6-8 times per hour
- Bathroom with shower – 15-20 times per hour
- WC – 6-10 times per hour
- Living room – 4-6 times per hour. This number is larger if the room is smoky
The
capacity of a fan is often defined as volume in cubic metres (cu m), or cubic feet (cu ft), per hour.
To
determine the minimum capacity of fan required, calculate the volume of the room (length x width x height) then multiply by the recommended number of air changes required (above).
Positioning the fan
Most obviously, the best place to position an extractor fan is either in
a window or an exterior wall. However, esthetical reasoning aside, this rule of thumb is often complicated by the location of the source of fresh air – or put simply the door.
A fan works best when sited opposite to the door to allow the air to circulate through the room from the door to the fan. In a kitchen the best site is often adjacent to, or over, the cooker to prevent steam from being drawn across the room.
- Always ensure that you check the chosen site of the fan using a pipe & cable detector to ensure that you do not drill through any water pipes or electrical cables.
- Do not position a fan too close to a door as this will provide air circulation at the door but have little of no effect on the rest of the room.
- If the room contains a fuel burning appliance, such as an aga, with a flue, you must ensure that there is adequate replacement air within the room to prevent fumes being drawn down the flue by the action of the extractor fan when it is switched on. The exception to this is if the appliance has a balanced flue which draws air from the outside, rather than from within the room.
