Installation guide

Direct Venting (Two-pipe System)
59
Vent Length Requirements (continued)
Maximum vent/air intake pipe length - horizontal/vertical (hybrid system)
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 lenghts. See
table 41, as well as fig 49 and 50 for
reference.
Table 41. Maximum allowable equivalent length - vertical exhaust /
horizontal air intake (hybrid)
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 vent with Ø 2” (CVPC, PVC, ABS) air intake pipe,
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 (see fig. 55). Minimum vent length is 3.3 ft. / 1m.
Legend
Support system
Flashings
Exhaust (straight coupling) with
screen
Combustion air intake with screen
a Equivalent length (exhaust)
b Equivalent length (air intake)
c min. 18” / max. 48”
5368 815 v2.0 b
Air
Vitodens
b
c
C
B
A
a
Fig. 53 Vitodens 100-W and 200-W BW2B 9-19/26/35
Flue
D