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Boiler manual: • Installation • Start-Up • Maintenance • Parts
31Part No. 550-110-275/1018
Connect breeching and venting systems
Seal the venting system gas-tight and connect the breech-
ing with welded seams and joints to prevent leakage of
combustion products into the boiler room. This is most
important for forced draft vent systems. Conventional
flue pipe should not be used as it could leak flue gases
and carbon monoxide emissions through seams and
joints, resulting in severe personal injury or death.
General venting information
1. Model 94 boilers operate with positive overfire pressure. Adjust
damper assembly (see Figure 44, page 35) during burner start-up
to achieve 0.1" W.C. positive pressure at damper sample hole.
Construct metal breeching:
1. 894-2194 boilers — construct "stub" to attach breeching:
a. Use steel breeching-16 ga. or heavier, 20" nominal diameter,
minimum 6-inch length (so damper can open).
b. Unbolt the breeching counter flange from flue collar flange.
c. Insert or butt the breeching stub against counter flange so
stub is square to flange. Stub must not extend past the face of
the flange.
d. Weld stub to flange gas-tight. Use caution when welding to
avoid warping the flange due to excessive heat accumulation.
1 Flue collar flange
2 Counter flange
3 (8) ½" x 1½" machine bolts,
nuts and washers
4 Sealing rope,
3
⁄8" diameter
5 Gas-tight weld to breeching
adapter pipe
6 20-inch diameter breeching
pipe, min. 6" long (by installer)
e. Make sure the sealing rope is intact on the flue collar flange.
f. Attach the flange/stub assembly to the flue collar using ½" x
1½" machine bolts and washers provided. The connection
must be gas-tight.
2. 2294-2594 boilers — attach factory-supplied breeching adapter:
a. The boiler is supplied with a flanged breeching adapter 22-inch
diameter x 12 inches long.
b. Make sure the sealing rope is intact on the flue collar flange.
c. Attach the flange/stub assembly to the flue collar using ½" x
1½" machine bolts and washers provided. The connection
must be gas-tight.
3. See Figure 39 for minimum breeching diameter.
4. Select material type and thickness in compliance with local
codes.
5. Refer to ASHRAE Guide for chimney and breeching calculations
and construction and lining.
Long horizontal breechings, excessive number of tees and
elbows or other obstructions restricting combustion gas
flow can result in possibility of condensation, flue gas
leakage and carbon monoxide emissions, causing severe
personal injury or death.
Figure 39 Minimum breeching diameter
Boiler
model
AHRI vent or
liner diameter
(inches)
Boiler
flue collar
dimensions
(inches)
Balanced
draft
(note 4)
Forced
draft
(note 3)
894
18
(note 1)
14
(note 1)
20 round, flanged
994
21
(note 1)
14
(note 1)
20 round, flanged
1094
21
(note 1)
16
(note 1)
20 round, flanged
1194
21
(note 1)
16
(note 1)
20 round, flanged
1294
21
(note 1)
16
(note 1)
20 round, flanged
1394
24
(note 1)
18
(note 1)
20 round, flanged
1494
24
(note 1)
18
(note 1)
20 round, flanged
1594
24
(note 1)
18
(note 1)
20 round, flanged
1694
24
(note 1)
18
(note 1)
20 round, flanged
1794
24
(note 1)
20 20 round, flanged
1894
27
(note 1)
20 20 round, flanged
1994
27
(note 1)
20 20 round, flanged
2094
27
(note 1)
20 20 round, flanged
2194
27
(note 1)
20 20 round, flanged
2294
27
(note 2)
22
20 round, flanged
(note 2)
2394
30
(note 2)
22
20 round, flanged
(note 2)
2494
30
(note 2)
22
20 round, flanged
(note 2)
2594
30
(note 2)
22
20 round, flanged
(note 2)
Note 1 Boiler is supplied with a counter flange that must
be welded to a 20-inch diameter x 6-inch minimum
length adapter. The breeching can then be reduced or
increased to the size listed above.
Note 2 Boiler is supplied with a flanged adapter, 22-inch
diameter, for connection to 22-inch diameter
breeching. Breeching size can be increased after the
adapter if required for the application.
Note 3 Forced draft — Boiler, breeching and stub vent
operate at positive pressure. Entire system must be
gas-tight to prevent leaks. Stub vent height must be
limited to prevent negative draft with 3-foot minimum
stub vent height above roof, 15-foot minimum overall
height. See Figure 41 and Figure 42.
Note 4 Balanced draft — Boiler operates with positive
pressure overfire. Chimney may provide excess draft
which may require a barometric draft control installed
and set to provide minimum draft to maintain 0.1"
positive pressure at flue collar. Minimum chimney
height above roof is 3 feet. Minimum overall height is
20 feet. For other vent heights, use ASHRAE Guide for
sizing. See Figure 40 and Figure 42.
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