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13
be limited to prevent negative draft with 3-foot minimum stub
vent height above roof. See Figures 31 and 32.
provide excess draft which may require a barometric draft con-
trol installed and set to provide minimum draft to maintain 0.1"
positive pressure at flue collar. Minimum chimney height above
roof is 3 feet. See Figures 33 and 34.
Stub vent – forced draft —
single boiler
Conventional chimney –
balanced draft with barometric
draft control when required —
single boiler
Part No. 550-141-935/0215
Stub vent – forced draft —
multiple boilers
Conventional chimney –
balanced draft with barometric
draft control when required —
multiple boilers
through seams and joints, resulting in severe
personal injury or death.
and construction and lining.
tees and elbows or other obstructions restricting
combustion gas flow can result in possibility
monoxide emissions, causing severe personal injury
or death.
Minimum breeching diameter —
forced draft venting
Boiler
AHRI recommended
model
minimum vent
number
diameter
(inches)
380
480
580
680
780
880
10
980
10
1080
10
1180
10
1280
12
Minimum breeching diameter —
balanced draft venting
Boiler
AHRI
model
round vent
number
diameter
(inches)
380
8
480
10
580
10
680
11
780
12
880
15
980
15
1080
15
1180
15
1280
15
Flue collar outlet
diameter
(inches)
6
8
7
8
8
8
8
8
9
10
10
10
10
10
12
AHRI
Minimum
Flue collar
rectangle
chimney/
outlet
chimney
vent
diameter
size
height
(inches)
(feet)
(inches)
8 x 12
15
8
8 x 12
15
8
12 x 12
15
8
12 x 16
15
8
12 x 16
15
10
12 x 16
15
10
16 x 16
15
10
16 x 16
15
10
16 x 16
15
10
20 x 16
15
12
31
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