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Venting The Heater - Bosch 125B LP Installation And Operating Instructions Manual

Automatic instantaneous type water heaters for use with natural and liquefied petroleum gas
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Expansion and contraction of piping due to changing water
temperature in the pipes imparts movement to the heater
which, if mounted directly to a brittle, friable board, such
as plasterboard, can cause failure of mounting.
In earthquake-prone zones, CEC recommends that
installers use a large washer and lag screw through the
existing holes used to hang the heater to affix the upper
third of the heater to the mounting board. To affix the lower
third of the heater, CEC recommends that two new holes
be drilled in the heater's frame, each one 16 inches below
the top two holes, and that washers and lag screws be
used to secure the lower portion of the heater to a spacing
Before installing the unit, be certain you have the correct
heater for your type of Gas – Propane or Natural Gas.
Identification labels are found on the shipping box, and on
the rating plate which is located on the right side panel of
the cover. Also, each burner orifice is stamped with a number
(79 for LPG and 120 for Natural Gas).
13 ¼"
Fig. 1 - Mounting the Heater
The incandescent particle tray (shipped loose in the carton
with the water heater) must be attached at the bottom of
the water heater front cover at the time of installation. Use
the screws provided. See figure 2
Fig. 2 - Incandescent Particle Tray Illustration
Vent pipe connection. WARNING: Do not reduce
the vent pipe size.
This appliance must be vented to the outside following all
local ordinances and specifications for installing a gas
appliance vent or chimney. The venting system must be
designed and constructed so as to develop a positive flow
adequate to remove flue gasses to the outdoors.Minimum
vent size must be 5". Minimum height must be 6 feet,
provided there are no elbows. Termination of vent
must be 2 feet above any obstruction within a 10 foot
Consult your gas utility or National Fuel Gas Code if
vent will have elbows or share venting with another
appliance. The vent connector should have as much
vertical rise as possible (minimum 12") before any
horizontal run.
The appliance must be located as close as practicable to
a chimney or vent. The vent pipe sections must be secured
to each other with sheet metal screws. Keep in mind the
minimum clearance from the top of your heater. Remember
also that single wall vent pipe connectors require a 6 inch
clearance from combustibles. National Fuel Gas Code
specifies double wall — Type "B" — vent pipe be used in
cold climates and for gas vents running through attics. We
consider double wall vent pipe preferable in all
circumstances. Any vent section greater than 45 degrees
from vertical is considered horizontal. Horizontal sections
of vent connectors must slope upwards at least 1/4 inch for
every foot of its horizontal length. Keep the horizontal section
short and avoid too many elbows.
Optional powervent available in order to sidewall vent.
Contact your local dealer.
To check the draft:
Close all doors and windows to the outside.
Turn on all appliances that force air out of the building.
These include all exhaust/ventilation fans, furnaces, clothes
dryers, wood burning stoves, etc.
Open all doors between the AquaStar and these other
Run the unit for at least 10 minutes. Then hold an ordinary
mirror at the side above the front shell. Any flue gases
1" X 4"
backdrafting will cause the mirror to fog. This is a serious
health hazard and must be corrected. Poor venting can
result in soot building up inside the heater, overheating of
the heater and freezing of the heat exchanger in a freezing
The mirror will remain clear with a properly functioning draft.
Note: The burners of an instantaneous "on demand" water
heater such as the AquaStar are only on at the time that
hot water is actually being used, the vent pipe is therefore
cold except for the short durations when hot water is being
used, it is therefore very important that the venting and air
supply be adequate to provide a good positive draft as soon
as the burners turn on. See venting guide on back page.
The AquaStar 125B instantaneous water heaters have built-
in draft diverters and are designed for indoor installation
only. The draft diverter outlet must be connected to a clear,
unobstructed vent of the same size, or larger.
In Canada, CAN/CGA-B149 Installation Code for detailed
In U.S.A., ANSI Z223.1 - NFPA 54, national Fuel Gas
Code for detailed requirements.
The vent connection for the AquaStar 125B is 5 inches.
However, IN CANADA, for installations at high altitude
(2000-4500 feet above sea level) a six inch flue is required.
A 5" by 6" flue adaptor must be affixed to the flue collar of
the AquaStar with at least two screws. See figure 3.

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