LAARS Heating Systems
Page 16
2.C.5.b Ducted Combustion Air
The combustion air can be taken through the wall, or
through the roof. The manufacturer offers accessories
to use with ducted air systems, as shown in Table 8.
See Table 7 to select the appropriate diameter air pipe.
When taken from the roof, a field-supplied rain cap or
an elbow arrangement must be used to prevent entry of
rain water. (See Figure 7).
Use ABS, PVC, CPVC, polypropylene, stainless steel,
or galvanized pipe for the combustion air intake (See
Table 7). The intake must be sized per Table 9. Route
the intake to the boiler as directly as possible. Seal all
joints. Provide adequate hangers. The unit must not
support the weight of the combustion air intake pipe.
The maximum equivalent pipe length allowed is 100 feet
(30 m).
Each elbow is considered to be 5 feet (1.5m)
When using polypropylene or stainless steel materials
in horizontal duct configurations, a single elbow must
be installed on the end of the air inlet to act as an
outdoor terminal. In vertical duct applications, two
elbows must be installed on the end of the inlet to act
as a vent terminal. When elbows are use as terminals,
appropriate screens must be installed to prevent
blockage.
The elbow(s) required for termination are not included in
the kits shown in Table 8
The connection for the intake air pipe is on the back
panel.
In addition to air needed for combustion, air shall also
be supplied for ventilation, including air required for
comfort and proper working conditions for personnel.
Refer to the applicable codes.
2.D Locating the Vent and Combustion Air
Terminals
2.D.1 Side-wall Vent Terminal
The appropriate side-wall vent terminal must be used.
The terminal must be located in accordance with
ANSI Z223.1/NFPA 54 and applicable local codes. In
Canada, the installation must be in accordance with
CSA B149.1 or .2 and local applicable codes.
Consider the following when installing the terminal:
1. Figure 6 on page 18 shows the requirements for
mechanical vent terminal clearances for the U.S.
and Canada.
2. Vent terminals for condensing units or units with
condensing vents are
not
permitted to terminate
above a public walkway, or over an area where
condensate or vapor could create a nuisance or
hazard.
3. Locate the vent terminal so that vent gases cannot
be drawn into air conditioning system inlets.
4. Locate the vent terminal so that vent gases cannot
enter the building through doors, windows, gravity
inlets or other openings. Whenever possible, avoid
locations under windows or near doors.
5.
Locate the vent terminal so that it cannot be
blocked by snow. The installer may determine
that a vent terminal must be higher than the
minimum shown in codes, depending upon
local conditions.
6. Locate the terminal so the vent exhaust does not
settle on building surfaces or other nearby objects.
Vent exhaust bi-products may damage surfaces or
objects.
7. If the boiler or water heater uses ducted
combustion air from an intake terminal located on
the same wall, see See Figure 6 on page 18 for
proper spacing and orientation.
