Flue Connection And Venting - Dunkirk D247 Installation Instructions Manual

FLUE CONNECTION AND VENTING
Consult local codes and gas company requirements.
Adhere to the following standard practice recommendations
for installing the flue pipe:
1 . Consult dimensional drawing for number and size of
flue pipes required for each size boiler.
2. Maintain minimum upward slope of 1/4 inch per linear
foot from the boiler to chimney.
3. Run flue pipe directly as possible. Keep turns to a
minimum. Insert flue pipe into, but not beyond, inside
wall of chimney. Do not connect into a chimney serving
an open fireplace.
4. Insulate flue pipe where it passes near combustible
material.
5. Rigidly support pipe with hangers and straps.
6. Extend chimneys at least 2 feet above any object within
radius of 15 feet, including roof.
7. Install a hood on all flue pipes which extend through
roof.
In most locations, the venting of a boiler relies on natural
draft. Inasmuch as the energy available from natural draft
is quite low, serious thought should be given to vent system
design, i.e., adequate size, use of gradual transitions, tees,
elbows, etc., close proximity of boiler and chimney. On all
boilers, the vertical risers must be at least as large as the
vent openings on the drafthood.
The boiler manufacturer makes no specific
recommendations regarding the application of draft
inducers that may be used with this boiler. If a draft inducer
is used, it is up to the installing contractor and the draft
inducer manufacturer to determine the proper application.
A simple vent system consists of a 6-foot minimum vertical
rise immediately off the drafthood, as shown in Figure 19.
Terminate this vertical flue above the building roof with a
suitable rain cap at least 2 feet above surrounding
obstructions, i.e., parapets, adjacent buildings, penthouses,
etc. This type of vent system applies to single-drafthood
boilers ONLY, and has limited practical use, because it is
restricted to single-story boiler rooms and because of the
problems encountered in roof flashing.
The vertical venting system shown in Figure 19 cannot be
used on multiple-base boilers because of the physical
interference of multiple rain caps.
For multiple-base boilers, the pant leg venting system
shown in Figure 20 can be applied, if desired.
The vent system shown in Figure 21 is commonly used.
With the vent diameters sized to match the flue outlets, a
minimum vertical rise of 4 feet above the drafthood must
be maintained for proper operation. See Page 4 for typical
chimney sizes. Requirements for this type of system are:
an adequately sized chimney, adequate combustion air,
and the outlet end of the horizontal run must be no more
than 6 feet from the chimney with no more than one 90 °
elbow in this run as shown.
For installations where the required minimum 4-foot vertical
rise cannot be maintained, the diameter of the horizontal
run must be increased one inch for each foot of riser
reduction. This procedure wilt reduce the resistance of the
system, and if the chimney is adequate the boiler wilt vent
properly.
In certain cases where these short rises of less than 4 feet
have been used, spillage of combustion products has
occurred at the drafthoods farthest from the chimney.
Assuming the chimney is adequately sized, one acceptable
method to correct this spillage problem is to permanently
baffle the riser(s) closest to the chimney to reduce the
excess of room air entering those drafthoods. DO NOT
BAFFLE ENOUGH TO CAUSE SPILLAGE. The use of
fixed baffles in the short risers above the boiler drafthood
are acceptable as spelled out in American National
Standard NFPA 54/ANSI Z223.1 National Fuel Gas Code,
latest revision.
Fabricate these fixed baffles, using 20-gauge steel. See
Figure 22. Permanently attach the baffle to the inside of
the riser(s). Trial and error will dictate the degree to which
each should be positioned to avoid drafthood spillage at
the far end of the boiler. Be careful to avoid bending the
fixed baffle so it will obstruct the flue gas flow in the
horizontal collector.
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FIGURE
19
-RODF LINE -PANTLEG
BOILER BBILER
16
FIGURE 21
R DIAMETER
, !_I _ i_1_ ¸_ ........ _ P_A. _ viE_
ENLARGED
FIGURE 22
Baffle Size (Inches)
Shown is suggested size of fixed
baffle for different size risers.