CDA CCA5/7 - Manual (Page 8)

Installation
When the extractor is to be installed above an electric hob, the minimum distance between the hob and extractor must
exceed 600mm (650mm is recommended).
When the extractor is to be installed above a gas hob, the minimum distance between the hob and extractor must
exceed 700mm (750mm is recommended).
If the instructions provided with your gas hob state that the required distance between the hob and extractor must
be greater than 700mm, then that is the distance that should be observed; this is a legal requirement and may lead to
your hob being disconnected from the gas supply and the installation being reported to RIDDOR (The height should be
measured from the top of the burners).
IN THE ABSENCE OF ANY INSTRUCTIONS SUPPLIED WITH THE GAS HOB, THE MINIMUM DISTANCE
BETWEEN THE HOB AND EXTRACTOR MUST BE AT LEAST 760mm.
The width of any hob must not be greater than the width of the extractor installed above it.