Venting a gas-fired system – Slant/Fin Gas Hot Water User Manual
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VENTING A GAS-FIRED SYSTEM
A boiler venting system provides an escape path for the products of
combustion. There are three major components for venting a gas-fired
Caravan: a draft hood for each module, a breeching manifold and a
chimney.
Draft Hood
The draft hood is part of each boiler module, although shipped in a
separate carton. It compensates for excessive draft that can be
caused by the venturi effect of winds passing over the top of the chim-
ney. The dimensional relationships between the draft hood, the boiler
and surface on which the boiler is mounted, are critical. These factors
are all interdependent in allowing the draft hood to function without
moving parts. Attempts to alter these dimensions can result in unsafe
operating conditions.
Note: When mounting the modules on a raised platform, be certain
the platform extends past the edge of the modules at least 3 inches
on all sides.
Breeching
Breeching is a term used to describe a manifold(s) that connects
individual boiler modules to a chimney. Breeching is usually construct-
ed of sheet metal having a smooth interior surface with all joints made
tight against leakage. Pitch breeching up toward chimney. Horizontal
breeching size should be maintained for the total length. Any transi-
tions should be made after 4 modules. Connection should be made at
a 45° angle in the direction of the chimney. See figure 10.
Run breeching as high as clearance permits to obtain maximum
vertical rise of individual boiler vents. Note that this does not alter
chimney height (the height from hood skirt to chimney top). The
portion of chimney height rising directly above each hood is most
effective in preventing spillage. When the boiler room is in unheated
space, insulate vent pipe and breeching to maintain flue gas temper-
ature and good chimney operation. It is not permitted to lower draft
hood skirt height to achieve pitch, or to compensate for low
ceilings. For some combinations of low chimneys, ceilings and long
breeching, a draft inducer may be needed. Inducers when required
are locally specified and warrantied. The breeching should extend
into, but not beyond, the chimney liner.
Chimney
Caravan gas-fired modular boilers operate efficiently with masonry or
prefabricated chimneys as well as with “Type B” or double-walled
metal vent pipe. This latter type of chimney construction is generally
the least expensive. Chimney height is usually governed by the
building height and the size of the boilers (see Table 1). However, the
chimney should be high enough to minimize the effects of turbulent
winds and pressure common near roof-top obstruction. A vent cap
should be used where permitted for additional protection against
adverse wind conditions and precipitation. The National Board of Fire
Underwriters recommend that the chimney should extend at least 3
feet above the roof and be 2 feet higher than any obstruction within 10
feet.
Sizing Horizontal Breeching Connectors and Chimneys for Gas-
Fired Systems
Horizontal breeching connectors shall be constant sized. The chimney
and the horizontal breeching connector are sized using Table 2.
When there are multiple banks of boilers, the horizontal breeching
connector for each bank is sized using Table 2. To size the common
horizontal breeching connector, add up the total input and refer to
Table 2 to size.
The minimum chimney opening will be equal to the size of the largest
horizontal breeching section connected to it.
Horizontal Breeching Connector Length
The MAXIMUM length of the horizontal breeching connector length
between the chimney and the closest boiler shall NOT be longer than
12 inches per inch of horizontal breeching connector diameter, i.e. if
the horizontal breeching connector is 16" D., the MAXIMUM length
from the chimney to the first boiler would be 16" x 12" or 192 inches.
The MINIMUM length shall be 12 inches regardless of the horizontal
breeching connector diameter. See figure 9.
GGT-600E
2
GG-300ES
12"
10"
10"
9"
GGHT-700E
2
GG-350HES
12"
12"
10"
10"
GGHT-750E
2
GG-375HES
12"
12"
12"
10"
GGHT-800E
2
GG-399HES
12"
12"
12"
10"
GGT-900E
3
GG-300ES
14"
12"
12"
12"
GGHT-1050E
3
GG-350HES
14"
14"
14"
12"
GGHT-1125E
3
GG-375HES
14"
14"
14"
12"
GGHT-1200E
3
GG-399HES
16"
14"
14"
12"
GGT-1200E
4
GG-300ES
16"
14"
14"
12"
GGHT-1400E
4
GG-350HES
16"
16"
16"
14"
GGHT-1500E
4
GG-375HES
16"
16"
16"
14"
GGT-1500E
5
GG-300ES
16"
16"
16"
14"
GGHT-1600E
4
GG-399HES
18"
16"
16"
14"
GGHT-1750E
5
GG-350HES
18"
18"
16"
14"
GGHT-1875E
5
GG-375HES
18"
18"
18"
16"
GGHT-2000E
5
GG-399HES
20"
18"
18"
16"
GGHT-2100E
6
GG-350HES
20"
18"
18"
16”
GGHT-2250E
6
GG-375HES
20"
20"
18"
16"
GGHT-2400E
6
GG-399HES
20"
20"
20"
18"
GGHT-2450E
7
GG-350HES
20"
20"
20"
18"
GGHT-2625E
7
GG-375HES
22"
20"
20"
18"
GGHT-2800E
7
GG-399HES
22"
22"
20"
18"
GGHT-2800AE
8
GG-350HES
22"
22”
20”
18”
GGHT-3000E
8
GG-375HES
24"
22"
22"
20"
GGHT-3150E
9
GG-350HES
24"
22"
22"
20"
GGHT-3200E
8
GG-399HES
24"
22"
22"
20"
GGHT-3375E
9
GG-375HES
24"
24"
22"
20"
GGHT-3500E
10
GG-350HES
24"
24"
22”
20"
GGHT-3600E
9
GG-399HES
26"
24"
24"
20"
GGHT-3750E
10
GG-375HES
26"
24"
24"
22"
GGHT-4000E
10
GG-399HES
26"
26"
24"
22"
Model No.
No. of
Modules
Module
No.
Consists of
Chimney Height*
20
Feet
25
Feet
30
Feet
50
Feet
Based on single row of modules with no elbows.
* Height measured from top of draft hood to top of chimney.
NOTE:
For conditions other than those shown, consult factory, or
National Fuel Gas Code NFPA 54
Table 2. Breeching dimensions for gas-fired systems
GGT and GGHT series: hot water boilers.