To limit the probability that water vapour will
condense on the interior surface of exhaust ducts, which could lead
to:
the deterioration of ducts, which could lead to the
blockage of ducts (e.g. ducts collapsing due to corrosion), which
could lead to inadequate ventilation, or
the generation of pollutants from biological growth.
This is to limit the probability of
negative effects on the air quality of indoor spaces, which could
lead to harm to persons.