Combustion Air Requirements - Bosch GWH 715 ES User Manual

3.4

Combustion air requirements

Warning: In areas where outside
temperatures routinely come close to
freezing, sealed combustion operation
is required. Use separate terminations
for combustion and vent, which must be
installed on the same wall or roof
surface, however never facing the
direction of prevailing winds. Failure to
do so may result in heat exchanger
freezing up and bursting. This failure is
not covered under the manufacturer's
warranty.
Warning: When
environment where corrosive chemicals
or dirty air are present the twin pipe
system is required.
Twin pipe
The GWH 715 ES is designed as a sealed combustion
appliance. It is recommended that the combustion air
be provided by a dedicated 3" or 4" pipe from the
outside. The combustion air pipe may be PVC or any
other rigid sealed 3" or 4" pipe. Horizontal sections of
the combustion air pipe must pitch down towards
termination 1/4" per foot to prevent rain water from
entering the appliance. The combustion air inlet,
whether terminating vertically or horizontally, must be
located in such a manner as to provide a
minimum 3 foot clearance from the exhaust vent
terminator. See Fig. 10 Letter I, page 12.
The maximum length of the combustion air inlet
is 26 feet with one elbow. Subtract 2.5 feet for
each additional 90° elbow and 1.25 feet for each
additional 45° elbow. Maximum number of
elbows permitted is 3.
Warning: Terminations must prevent
rain and debris from entering the
combustion air and exhaust vent piping.
Single pipe
Note: This appliance requires 9950 cubic feet of
available combustion air, or a minimum of 1243
square feet of space with an 8 foot ceiling to
operate. If the large amount of air space, which
equates to about half of most average sized
homes, is not available, the appliance must pull
air from the outside (see twin pipe above).
Although it is permissible to draw combustion air from
inside the structure, it is not the manufacturer's
recommended installation method. Always install a 3
inch elbow on the top of the combustion air inlet
adaptor to prevent foreign objects from falling into the
unit.
If a single pipe installation is utilized, follow guidelines
6 720 608 158
installed in an
below for providing adequate combustion air for the
water heater as well as any other appliances that may
consume air in the space. Always follow local codes if
they are more stringent.
This Installation Manual specifies the minimum vertical
vent pipe and the amount of combustion air required for
this unit. When all requirements are followed, the unit
will operate properly and safely. However, there may still
be a risk of freezing due to negative draft if the other
combustion appliances in the building are not supplied
with sufficient combustion air. A wood stove or furnace
can pull its combustion air from the heater's vent pipe,
allowing the cold incoming air to freeze the cold water
in the heat exchanger. Supplying more combustion air
for all combustion appliances is the solution. A HVAC
specialist should be consulted to design solutions for
providing more combustion air.
Observe the following guidelines:
Installations in structures that have been tightly
constructed (air infiltration rate of 0.40 ACH or less)
must be provided with combustion air per the National
Fuel Gas Code. Consult a HVAC specialist if your air
infiltration rate is questionable.
The space must have two permanent openings, one
commencing within 12 inches of the top and one
commencing within 12 inches of the bottom of the
enclosure.
Each opening must have a minimum free area of one
square inch per:
• 1000Btu/hr if all air is taken from inside the building
• 2000Btu/hr if all air is taken from the outside by
horizontal ducts
• 4000Btu/hr if all air is taken from the outside by
direct openings or vertical ducts.
Or the space must be provided with one permanent
opening or duct that is within 12 inches of the ceiling of
the enclosure.
This opening must have a minimum free area of one
square inch per:
• 3000Btu/hr if all air is taken from the outside by a
direct opening or vertical duct.
Louvers, grills and screens have a blocking effect. If the
effective free area in not known, increase the sizes of
your openings by 300% if your louvers are wood and by
43% if your louvers are metal. Refer to National Fuel
Gas Code for complete information.
3.5 Proper location for installing your
heater
Carefully select the location of the water heater. For
your safety and for proper heater operation, you must
provide combustion air to the heater and a proper
exhaust vent system.
Follow the guidelines below:
Installation instructions
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