Miele KMDA 7774 Operating And Installation Instructions page 12

Warning and Safety instructions
In order to ensure safe operation and to prevent gases given off by
the heating appliance from being drawn back into the room when
the extractor and the heater are both operated simultaneously, an
underpressure in the room of 4 Pa (0.04 mbar) is the maximum
permissible.
Sufficient ventilation can be maintained by air inlets which cannot
be blocked, e.g. in windows, doors and outside wall vents. The
diameter of the inlet openings must enable sufficient ventilation. A
ventilation brick alone is not generally sufficient to ensure safe
ventilation.
The overall ventilation condition of the dwelling must be taken into
account. If in any doubt, the advice of a competent builder or, for
gas, a qualified gas fitter (registered with an official gas safety
body in accordance with national safety regulations) must be
sought.
If the extractor is being operated in recirculation mode, where the
air is directed back into the room in which it is located, operating a
heating appliance which depends on the room air at the same time
is not hazardous.
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