The diameter of the outlet hole should never be reduced more than 20% of the original diameter. Reducing it by more than 20% will significantly decrease the performance of the hood and increase the noise level. For example, if the outlet hole is 150 mm, the section can be reduced to 125 mm at the most. If the outlet hole is 125 mm, it can be reduced to 100 mm. In some models, it is not possible to reduce the diameter of the fumes outlet hole, so we recommend checking the indications in the manual which can be downloaded from the Elica website in the product data sheet of the relevant model.