C13
Flue gas exhaust and air suction duct
through external wall in the same range
of pressure
C 33
Flue gas exhaust andair suction duct from
outsidewithroof terminalin the same
range of pressure
C53
Flue gas exhaust leading outside and air
suction duct through external wall not in
the same range of pressure
S1 = Air intake S2 = Flue gas exhaust
S1 = S2 - Air intake and ue gas exhaust equal lengths
S1 + S2 - Air intake and ue gas exhaust unequal lengths