Combustion Air Requirements - Bosch GWH C 920 ES Instruction Manual

Installation instructions
3.4

Combustion air requirements

Warning: In areas where outside
temperatures routinely come close to
freezing, sealed combustion operation
is required.
termination or 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.
When
Warning:
environment where corrosive chemicals
or dirty air are present, the twin pipe or
concentric vent system is required.
Twin pipe
The tankless water heater 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. The combustion
air piping must pitch down ¼ inch per foot towards
termination 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 any exhaust vent terminator.
See table 4 for combustion air piping specifications.
Warning: Terminations must prevent
rain and debris from entering the
combustion air and exhaust vent piping.
Single pipe
Note: This appliance requires 11,250 cubic feet of
available combustion air, or a minimum of 1,406
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
the inside, it is not the manufacturer's recommended
installation method. Always install a 3 inch 90° 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
below for providing adequate combustion air for the
water heater as well as any other appliances that may
consume air in the same space. Always follow local
codes if they are more stringent and regulations.
• Appliances located in unconfined spaces:
20
Use a concentric
installed in an
– a) An unconfined space is one whose volume is
greater than 50 cubic feet (1.42 cubic meter) per
1000 Btu per hour (292.81 Watts) of the
combined rating of all appliances installed in the
space. That would be 11250 cubic feet (318.6
cubic meters) for the GWH C 920 ES alone.
– b) In unconfined spaces in buildings of
conventional frame,
construction, infiltration air is normally adequate to
provide air for combustion.
• Appliances located in confined spaces:
The confined space must be provided with two per-
manent openings, one commencing within 12 inches
(304.8mm) of the top and one commencing within
12 inches (304.8mm) of the bottom of the enclosure.
Each opening must have a minimum free area of one
square inch per:
– 1000 Btu/hr (292.81 Watts) if all air is taken from
inside the building
– 2000 Btu/hr (585.62 Watts) if all air is taken from
the outside by horizontal ducts
– 4000 Btu/hr (1171.24 Watts)if all air is taken from
the outside by direct openings or vertical ducts
Or the confined space must be provided with one
permanent opening or duct that is within 12 inches
(304.8mm) of the ceiling of the enclosure. This opening
must have a minimum free area of one square inch per:
– 3000 Btu/hr (878.43 Watts) if all air is taken from
the outside by a direct opening or vertical duct.
Louvers, grills and screens have a blocking effect, when
used, increase the sizes of your openings by 300% for
wood louvers (as wood type will reduce the free air by
75%) and 43% for metal louvers (as metal will reduce
the free air by 30%). Refer to the National Fuel Gas
Code for complete information. In buildings of tight
construction all air should be taken from outside.
masonry, or metal
6 720 608 836