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Combustion Air Requirements - Bosch Pro Tankless GWH-450-ES Series Manual

Temperature modulated with electronic ignition - normal duty suitable for recirculating potable water only
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Installation instructions
Fig. 7
Mounting the water heater
3.5

Combustion air requirements

Warning: In areas where freezing
temperatures are common the twin pipe
system is recommended. A negative air
condition may result in cold air being
drawn across the heat exchanger coil
causing it to freeze and burst. This
failure is not covered under the
manufactures warranty.
Warning:
When
environment where corrosive chemicals
or dirty air are present the twin pipe
system is required.
Twin pipe
The GWH-450-ES is designed as a sealed combustion
appliance. It is recommended that the combustion air
be provided by a dedicated 3" pipe to the outside. The
combustion air pipe may be constructed of aluminum
flex, PVC or any other rigid or semi rigid sealed 18 inch.
The combustion air inlet should be located in such a
manner as to provide a 3 foot clearance from the
exhaust vent terminator. See Fig. 18 Letter I.
The maximum length of the combustion air inlet is 39
feet with one elbow. Subtract
elbows. Maximum number of elbows permitted is 4.
Single pipe
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 elbow on the
10
installed
in
an
6
feet for additional
top right side of the combustion air inlet to prevent
foreign object from falling into the unit (see Fig. 17).
If a single pipe installation is performed. Use the
following
guidelines
combustion air for the recirculating water heater as well
as any other appliances that may consume air in the
space. Always follow local codes if more stringent.
• Appliances located in unconfined spaces:
– 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 6200 cubic feet (175.6
cubic meter) for the GWH-450-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 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.
Louvers, grills and screens have a blocking effect, when
used, increase the sizes of your openings by 400% for
wood louvers (as wood type will reduce the free air by
75%) and 135% 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.
when
providing
adequate
masonry,
or
6 720 607 915
metal

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