Installation guide

Direct Venting (Two-pipe System)
56
Vent Length Requirements
Maximum vent/air intake pipe length - horizontal
The total equivalent length specified for
a two pipe system is the total
combined length of the exhaust vent
and air intake pipe system. Do not
exceed these maximum lengths. See
table 39 and fig. 49 and 50 for
reference.
Table 39. Maximum allowable equivalent length - horizontal
Boiler Model
System Ø
See note
below
Max. combined
equivalent
vent length (a+b)
*2
HWB1B 10-26, 10-35 2” / 51mm
3” / 76mm
*1
4” / 102mm
*1
86ft. / 31m
164ft. / 50m
200ft. / 61m
HWB2B 9-19/26/35 2” / 51mm
3” / 76mm
4” / 102mm
115ft. / 35m
148ft. / 45m
180ft. / 55m
HWB2B 17-45, 17-60 3” / 76mm
4” / 102mm
98ft. / 30m
148ft. / 45m
HWB2B 30-80, 30-105 4” / 102mm 131ft. / 40m
*1
2” to 3” or 2” to 4 “ increaser field supplied. Do not order Viessmann 3” or 4” starter adaptor.
*2
See figure 49 and 50
Note:
For combination of different vent/air intake pipe diameters, such as Ø 3” stainless steel
ventwithØ2”(CVPC,PVC,ABS)airintakepipe, the total equivalent length must be
used for the smaller pipe diameter.
Maximum of five 90° elbows allowed in the entire vent and air intake system
(first 90º elbows are not included see fig. 55). Minimum vent length is 3.3 ft. / 1m.
Legend
Support system
Exhaust pipe termination with
screen
Combustion air intake with screen
a Equivalent vent length (exhaust)
b Equivalent vent length (air intake)
5368 815 v2.0 b
IMPORTANT
Always include vent termination
length in calculations.
Support
System
Support
System
B
Side Wall
Caulk here
(exterior caulking)
Air
Vitodens
Fig. 49 Vitodens 100-W and 200-W WB2B 9-19, 9-26, 9-35
Flue
C
b
a
Flue starter adaptor
Boiler vent pipe adaptor
Air intake starter adaptor
A
Field supplied
Exhaust/Air
intake pipe
fittings