10 111924-01 - 2/23
8HE Multiple Boiler Application Instructions
2Venting
WARNING
Asphyxiation Hazard.
•Failure to vent this boiler in accordance with these
instructions could cause products of combustion
and/or carbon monoxide to enter living space,
resulting in severe personal injury, death or
substantial proper damage.
•Vent installation shall be in accordance with local
codes, authority having jurisdiction, National Fuel
Code - ANSI Z223.1/NFPA 54, ASHRAE Handbook,
or applicable requirements of the local building
codes.
•Inspect existing chimney before installing boilers.
•Maintain clearances to vent piping and draft hood.
•Do notalter boilerdraft hoodor placeany obstruction
or non-approved damper in the breeching or vent
system.
!
WARNING
Vent system must not experience signs of
continuous wetness.
!
2.1 Avoiding Flue Gas Condensation
Masonry chimneys, and in particular exterior masonry
chimneys, are more susceptible to the formulation of
condensate. If a masonry chimney experience signs
of continuous wetness, a listed metal liner must be
installed or an alternate vent system must be used. All
masonry chimneys must use either a clay tile liner or
listed metal liner.
Recommend use of listed metal chimney liner with
external masonry chimneys.
For external masonry chimneys that do not include a
listed metal chimney liner:
• Recommend double wall vent connectors
and double wall vent manifolds. Use only
double wall material on long runs.
• For common vent installations with 5 or 6
boilers, recommend sequencing boilers
to fire minimum of 2 boilers simultaneously.
Up to eight boilers may be vented into a
single vent system if a minimum of two
boilers are fired simultaneously. See also
Section 5 – Controls.
See also Section 3, Water Piping, for methods to
avoid flue gas condensation from low return water
temperatures.
2.2 General
Vent systems are generally less flexible in design
location than are water pipes, gas pipes or electrical
lines. To avoid conflicts for a given location, design
and layout the vents in this section before proceeding
to other sections of this manual. If the factory
fabricated water manifolds are to be used, boilers
should be laid out with 28½ in. spacing.
Vent terminations - provide clearances as shown
in Figure 2-3 and Figure 2-4 to minimize adverse
wind effects or pressure areas which may reduce
or impede vent flow. A UL Listed vent cap is also
recommended to minimize adverse wind effects.
Follow manufacturer’s instructions of venting system
components in addition to National Fuel Gas Code
- ANSI Z223.1/NFPA 54, ASHRAE Handbook, or
applicable requirements of local building codes.
Vent system design must address the following:
• Support of lateral runs so that vent pipe does
not sag.
• Support of common vent where it passes thru
a ceiling or roof.
• Firestops
• Flashing and storm collars.
• Guying or bracing of common vent pipe
above roof.
• Securing and gas tightness of joints.
• Lightning arrester if top of metal vent is one of
the highest points on the roof.
• Support of common vent where it passes thru
a ceiling or roof.
• Proper insertion of vent connection at
masonry chimney – vent should enter
chimney at a point above the extreme bottom
of chimney – vent should be flush with inside
of chimney and sealed (see Figures 1-3 and
1-4).
• Never connect a gas vent to a chimney
serving a fireplace unless the fireplace has
been permanently sealed.
• Never pass any portion of a vent system thru
a circulating air duct or plenum.
2.3 Clearances
See Table 2-2 for minimum clearances around
boilers to combustible materials and for service
access. Provide thimbles through combustible
construction.
