Bosch Model GWH 425 - Manual (Page 9)

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Installation instructions
9
3.6 Venting
B Minimum vent pipe diameter: 5 inches
B Minimum vertical vent height: 6 feet, with no elbows
B Establish 12 inch rise before any elbow
The heater must be vented to the outside following all
local ordinances and specifications for installing a gas
appliance vent or chimney. The heater must be located
as close as practicable to a vertically rising chimney or
vent that has a listed vent cap at its termination point.
The venting system must be designed and constructed
so as to develop a positive flow adequate to remove flue
gasses to the outdoors. Consult the National Fuel Gas
Code if the vent will have elbows or share venting with
another natural draft appliance.
3.6.1 Horizontal venting
A power vent, with a proof-of-draft safety interlock
device, is required and is available for sidewall venting.
Contact your dealer. In the Commonwealth of
Massachusetts power vented applications must utilize
proof-of-draft safety interlock device.
3.6.2 Vertical venting
B A 5 inch diameter gas vent constructed of double
wall Type B gas vent is recommended. A 6 inch vent
is required in elevations greater than 2000 feet, see
Fig. 10. Under no circumstances should the vent
pipe be reduced in size.
B An approved gas vent connector must be attached
to the top of the water heater and rise vertically at
least 12" before entering into an approved gas vent
connector elbow.
B The minimum vertical gas vent height allowed is 6
feet; horizontal vent connectors and elbows are not
to be considered in the total gas vent height.
B All gas vent sections must be secured to each other
with sheet metal screws and be properly supported.
Horizontal runs:
Any gas vent section that is greater than 45 degrees
from the vertical is considered horizontal. Horizontal
sections must slope upwards at least ¼ inch for every
foot of its horizontal length and be properly supported.
Keep the horizontal section short and avoid too many
elbows. The maximum horizontal run allowed is half of
the total vertical vent height; horizontal vent connectors
and elbows are not to be considered in the total gas
vent height.
Vent termination:
The gas vent constructed of double wall Type B gas
vent must terminate above the roof surface with a listed
vent cap at a height that's in accordance with Fig. 11
and table 2, provided it is at least 8 feet (2.4 m) from a
vertical wall or similar obstruction. All other gas vents
that are not able to terminate within the minimum
specified height allowed must terminate not less than 2
feet (0.6 m) above the highest point where it's passed
through the roof and at least 2 feet (0.6 m) higher than
any vertical wall or similar obstruction within 10 feet (3.1
m).
Fig. 9 Flat roof
Fig. 10 Vent Adaptor for High Altitude Installations
Danger: Do not reduce the vent pipe
size. Do not put an elbow directly on top
of heater. Failure to follow venting
requirements may cause dangerous
exhaust gases to enter living space.
Warning: Do not combination vent with
a mechanically vented appliance.
Warning: Horizontally venting to a
vertically constructed vent stack along
an outside wall of a building is not
permissible.
Warning: Horizontally venting to a
sidewall vent terminator (without power
vent) is not permissible
LISTED VENT CAP
MINIMUM 6
FEET (1.8M)
LISTED GAS VENT
ESTABLISH A ONE
FOOT RISE BEFORE
ANY ELBOWS
5” X 6” ADAPTOR
USED ON HIGH
ALTITUDE