Atag ES9011QM Mode D'emploi page 39

installation
discharge opening
GB 8
Bear in mind any local regulations concerning the ventilation
of gas appliances.
We advise the use of as large a discharge duct as possible.
A duct with a smaller diameter will have a low extraction
capacity and produce higher noise levels.
Bends produce resistance. Make sure that the duct has a
smooth run and has as few bends as possible. Draw the
flexible pipe out as far as possible.
The discharge stump has a diameter of 150 mm. It is best if
the discharge pipe also has this diameter.