It is necessary to choose a fan or fans for the duty to be performed. The calculation is based on the volume of the room and the rate of air change required.
Example A combined bathroom and W.C. measuring 2.14 m×2.14 m×2.44 m high=11.2 cubic
metres Number of air changes per hour=20 Air/movement required:-11.2×20= 224 m3/h or 0.062 m3/second Fan required e.g. Xpelair FXC6 (150 mm) extracting 0.063 m3/sec. or Vent-Axia (150 mm)
extracting 198 m3/h or 0.06 m3/s @ low speed and 284 m3/h or 0.08 m3/s @ normal speed.