Venting For Multiple Units - CleaverBrooks CFC-500 Operation, Service And Parts Manual

Section 3 — Stack and Intake Vent Sizing and Installation
3-12
G. VENTING FOR MULTIPLE UNITS
Cleaver-Brooks recommends that each Model CFC in a multiple
boiler installation be vented individually. If it becomes necessary to
connect multiple boilers to a common breeching, measures should
be taken to ensure an unrestricted flow of flue gas from each boiler.
An active draft inducer is recommended when venting multiple
boilers. In the absence of a draft inducer, ductwork sizing and
connections require special attention.
Use 'wye' connections (not 'tees') to connect each boiler to the
common breeching (see Examples 1 and 2 below).
B r e e c h i n g s h o u l d b e s i z e d u p w a r d w h e n n e c e s s a r y t o
accommodate additional boilers (see Example 3). As a rule of
thumb, the cross-sectional area of any ductwork downstream of a
wye connection should be equal to or greater than the combined
area of the incoming vent sections.
When multiple boilers are connected in a CB Falcon-controlled lead/
lag network, a 'Fan rate during off cycle' feature is available. When
a boiler goes off line and completes a post purge, the fan will
continue to run at a user-selectable rate. This feature provides a
further measure to prevent flue gas from flowing back into the boiler.
EXAMPLE 1
GOOD
BAD
6"
10"
o
45
6" 6"
14"
6"
Part No. 750-263