Minimising noise impact from mechanical ventilation

The main issues in minimising the noise impact of the ventilation system are the noise from the fan unit entering the ducts, the attenuation provided by the ducts, bends and junctions, and the characteristics of the room grill. The noise breaking out of the fan unit casing may also be significant in adjacent rooms. Whilst it is not a requirement of the regulations, reasonable provision should be made to limit the noise of mechanical extract fans. The noise index LAeq,T is used in BS 8233, where T is the duration of the measurement. If the noise from the sound source is steady (e.g. fluctuating by up to 3 dB) a measuring time of 1 minute will be adequate and the LAeq,1 min level will be similar to the dB(A) level used elsewhere. If the noise from the sound source fluctuates more than this a longer measuring time (T) will be required.