Vent Length; Equivalent Vent Length Calculation Example - Viessmann Vitocrossal 300 CU3A Installation Instructions Manual

CU3A Venting Systems Installation
Venting Length

Equivalent vent length calculation example

2 x 87º elbow...........................................3.2 ft. (1 m)
2 x vent pipe (1 m)....................................6.6 ft. (2 m)
1 x vent pipe (0.5 m)..............................1.6 ft. (0.5 m)
1 x vent termination................................2.4 ft. (0.73 m)
.
Total equivalent length...........................13.8 ft. (4.23 m)
IMPORTANT
First elbow is excluded from in equivalent vent calculation.
Always include vent termination length in calculations.
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.
Side Wall Vent Installation (Coaxial)
Coaxial adaptor installation
Note: This installation procedure is only required for the
CU3A 45, 57 and not for the CU3A 26, 35.
1. Remove the inspection port bolt 1 from the top of
the vent connection (as shown).
2. Fully insert the coaxial adaptor into the boiler.
3. Mark the center of the inspection port on the adaptor.
4. Remove the coaxial adaptor from the boiler and drill a
f in. hole where marked.
5. Deburr the edges of the drilled hole.
6. Fully install the coaxial adaptor into the boiler and align
the inspection port hole to the coaxial adaptor hole.
7. Reinstall the inspection port bolt 1 and tighten bolt
to seal.
Boiler model
CU3A 26, 35 98 ft. (30 m)
CU3A 45, 57
Do not exceed the maximum vent length.

First 87º elbow on boiler is not included in equivalent

vent length calculation.
Type of fitting
87º elbow/
87º inspection tee
45º elbow
A 10% boiler input reduction @ 30 m for all sizes and all
configurations.
Vent diameter
100/150
80/125 or
110/160
108 ft. (33 m)
-- 98 ft. (30 m)
Equivalent length
1.6 ft. (0.5 m)
1 ft. (0.3 m)
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