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Combustion Air Requirements; Venting - Bosch Aquastar GWH 1600 H N User Manual

Hydro-generated ignition suitable for heating potable water only not approved for space heating or preheated water applications
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Installation instructions

Combustion air requirements

The AquaStar water heater holds cold water in its
copper heat exchanger and water valve when not in use.
Because of this, any cold air that comes down through
the unit's vent pipe is capable of freezing these
components. 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 all the combustion appliances in
the area are not being supplied with a sufficient amount
of make-up air. A wood stove or furnace can rob the
makeup air in the AquaStar's vent pipe, leaving the cold
infiltrating air capable of freezing the cold water in the
AquaStar heat exchanger. Supplying more combustion
air for all combustion appliances is the solution. Follow
the instructions on venting and checking adequacy of
make up air. A HVAC specialist should be used to
design solutions for providing more make-up air if
concerning combustion air.
Appliances located in unconfined spaces:
a) An unconfined space is one whose volume is greater
than 50 cubic feet per 1000 Btu per hour of the
combined rating of all appliances installed in the space.
That would be 5850 cubic feet for the AquaStar GWH
1600 H alone.
b) Installations in structures that have been tightly
constructed (air infiltration rate of 0.40 ACH or less)
must be provided for combustion air per the National
Fuel Gas Code. Consult a HVAC specialist if your air
infiltration rate is questionable.
Appliances located in confined spaces:
The confined space must be provided with 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:
• 1000 Btu/hr if all air is taken from inside the building.
• 2000 Btu/hr if all air is taken from the outside by
horizontal ducts.
• 4000 Btu/hr 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 of
the ceiling of the enclosure. This opening must have a
minimum free area of one square inch per:
• 3000 Btu/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 is not known, increase the sizes of
your openings by 400% if your louvers are wood and by
135% if your louvers are metal. Refer to the National
Fuel Gas Code for complete information. In buildings of
tight construction all air should be taken from outside.


Danger: Do not reduce the vent pipe
size. Do not put an elbow directly on top
of heater. Failure to follow venting
requirements may result in dangerous
exhaust gases to enter living space.
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.
Warning: Do not combination vent with
a mechanically vented appliance.
Horizontal venting
Warning: Horizontally venting to a
vertically constructed vent stack along
an outside wall of a building is not
Warning: Horizontally venting to a
sidewall vent terminator (without power
vent) is not permissible.
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 Massa-
chusetts power vented applications must utilize proof-
of-draft safety interlock device.
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. 4. 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.
6 720 608 032

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