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A. Vent System Design
There are three basic ways to vent this boiler:
• Horizontal (“Side Wall”) Concentric Venting - Vent system exits the building through an outside wall. Concentric
venting consists of a “pipe within a pipe”. Flue gas exits the building through the inner pipe and combustion air is
drawn into the boiler through the space between the inner and outer pipe.
• Horizontal (“Side Wall”) Twin Pipe Venting - Vent system exits the building through an outside wall. Combustion air
and fl ue gas are routed between the boiler and outdoors using separate pipes.
• Vertical Twin Pipe Venting - Vent system exits the building through a roof. Combustion air and fl ue gas are routed
between the boiler and outdoors using separate pipes.
All of these systems are considered “direct vent” because in all of them, air for combustion is drawn directly from the
outdoors into the boiler. A description of all of these venting options are shown in Tables 7.1 and 7.8. For clarity, these
vent options are numbered from 1 to 6. One of the vent option columns in Tables 7.1 or 7.8 must match the planned vent
and air intake system exactly. In addition, observe the following guidelines:
1) Approved vent systems - Use only one of the approved vent systems shown in Tables 7.4 or 7.5. These vent systems fall
into two basic categories:
• Concentric Vent System - The standard boiler is supplied with a concentric vent system having a maximum usable
length of 25” (Figure 1.1). For longer runs, additional straight lengths and elbows are available from U.S. Boiler. Each
U.S. Boiler concentric vent component consists of an inner pipe of polypropylene and the outer pipe of steel. Integral
gaskets on each concentric fi tting provide a gas tight seal. A list of all U.S. Boiler concentric vent components is
shown in Table 7.4.
In this manual, concentric pipe sizes are called out in terms of the inner and outer pipe nominal diameters in
millimeters. For example, “60/100mm” pipe consists of a 60mm exhaust pipe inside a 100mm diameter outer pipe.
• Twin Pipe Vent Systems - Approved vent systems are made of a special stainless steel alloy (AL29-4C) for protection
against corrosive fl ue gas condensate. They are designed to provide a gas tight seal at all joints and seams so that fl ue
gas does not enter the building. Each approved vent system has a unique method for installation - do not attempt to
mix components from different vent systems. A list of approved twin pipe vent systems is shown in Table 7.5. Note
that a special vent collar (U.S. Boiler P/N 101004-01) is required if the boiler is to be vented with one of the approved
stainless vent systems.
2) Maximum Vent and Air Intake Lengths - The maximum length of the vent air intake piping depends upon the vent option
selected and the boiler size. See Table 7.1 or 7.8 for the maximum vent length. In horizontal vent systems, the lengths
VII Venting
WARNING
FAILURE TO VENT THIS BOILER IN ACCORDANCE WITH THESE INSTRUCTIONS COULD
CAUSE FLUE GAS TO ENTER THE BUILDING RESULTING IN SEVERE PROPERTY DAMAGE,
PERSONAL INJURY, OR DEATH:
* Do not attempt to vent this boiler with galvanized, PVC, or any other vent system not listed in
Table 7.6
* Do not attempt to mix components from different approved vent systems.
* Do not obtain combustion air from within the building.
* Do not install a barometric damper or drafthood on this boiler.
CAUTION
Moisture and ice may form on the surfaces around the vent termination. To prevent
deterioration, surfaces should be in good repair (sealed, painted, etc.)