In those cases where the noise index is a factor conditioning the installation and attenuation of the ventilator noise is required.

The design permits manufacture in different lengths and insulation thicknesses, adapting to the noise levels required in each case. In these models the housing is constructed from double metal lining plates, the inner plate being perforated. The space between both plates is filled with absorbent material. This feature enables the fan to be much more silent than one with a normal metal housing.

For maximum noise damping the length of the muffler housing must be at least 1.5 times the diameter of the fan.