False hood canopy depth for range cooker

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Are you intending to fit an extractor in this canopy? If so that would govern the depth of the canopy itself.

Also check the manufacturer's instructions for the minimum height at which it can be installed. If it's a dual fuel range I'm guessing gas rings therefore would be a minimum of 750mm high. I always find this a little low, especially for tall people so I tend to set it at about 850mm.

400mm depth should be adequate.