Miele DGC 6800 Operating And Installation Instructions page 165

Ventilation cut-outs
To ensure the appliance has adequate ventilation, the following cut-outs
measuring 500 x 40 mm must be provided:
in the top of the housing unit
in the interim shelf above the building-in niche
The furniture housing unit must not have a back panel fitted behind the building-in
niche.
Ventilation cut-out for the oven:
Please refer to the Installation instructions for the oven.
Appliance and building-in dimensions
165