Vent Length Requirements; Maximum Vent Length With Increasers; Maximum Vent Length; Minimum Vent Length - Viessmann Vitocrossal 300 CU3A Installation Instructions Manual

CU3A Venting Systems Installation

Vent Length Requirements

Maximum vent length with increasers

Coaxial increaser for systems
80/125 to 100/150 or 110/160
Vent length "a"
Legend
A Combustion air
B Boiler flue gas termination
C Coaxial adaptor (Vent manufacturer)
D Increaser
E 90° elbow
F Straight pipe (long)
G 45º elbow
H Straight pipe (short)
I Vent termination
J Roof flashing and storm collar
Note: Depending on the selected vent manufacturer,
a service clearance of 36 in. may be required.
Consult the vent manufacturer if using two-pipe
to coaxial adaptor directly at the back of the boiler.
Vertical Vent Installation (Coaxial)

Maximum vent length

Model No.
System vent size
Max. vent length "a" ft. (m)
* 1 If used with increasers 100/150,110/160
Model No.
System vent size
Max. vent length "a" ft. (m)

Minimum vent length

The minimum equivalent vertical vent length for all models
is 4 ft. (1.2 m) (=length of vent termination).
IMPORTANT
Always include vent termination length in calculations.
Type of fitting
87º elbow/
87º inspection tee
45º elbow
Note: First elbow not included in equivalent vent calculation.

Equivalent vent length calculation example:

2 x 87º elbow............................................3.2 ft. (1 m)
2 x 45º elbow............................................2 ft. (0.6 m)
3 x vent pipe (short)................................4.8 ft. (1.5 m)
1 x vent pipe (long)....................................3.3 ft. (1 m)
1 x telescopic extension (average length)...1.0 ft. (0.31 m)
1 x vent termination...............................4.2 ft. (1.28 m)
Total equivalent length..........................18.6 ft. (5.67 m)
CU3A 26, 35
80/125 100/150* 1
110/160
98 (30) 110 (33)
CU3A 45, 57
80/125 100/150
110/160
-- 98 (30)
Equivalent length
1.6 ft. (0.5 m)
1 ft. (0.3 m)
23