Bosch Appliances 125FX NG Water Heater User Manual

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WARNING: Do not reduce the vent pipe size and
do not common vent with any other vented appliance or
This appliance must be vented horizontally to the outside
with a sealed 4” single wall vent pipe. The appliance’s flue
gasses are under positive pressure and must travel through
a single wall 4” pipe that is sealed gas tight. The 4” single
wall vent pipe can be either stainless steel (AL29-4C) or
galvanized steel with at least 26 gauge. BBTNA recommends
the use of stainless steel vent pipe (which is equipped with
sealing gaskets) for ease of installation and durability. When
using galvanized vent pipe a minimum of 4 sheet metal
screws per connection must be installed and all seams must
be sealed with an approved high temperature silicone
sealant. The vent system must be gas tight. See Fig. 4 for
suggested venting installation diagrams.
The 125FX shall not be vented in combination with any
other appliance. This appliance may only be vented
horizontally with a dedicated sealed single wall vent. The
125FX shall not be vented into masonry chimneys or existing
vertical vents of any material.
CAUTION: 125FX vent system must be installed by a qualified
agency in accordance with these instructions. If improperly
installed a hazardous condition such as explosion or Carbon
Monoxide poisoning could result. BBT North America will
not be responsible for improperly installed appliances.
Establish vent clearances that comply with vent
manufacturer’s specifications. In all cases follow local codes.
See table below.
The vent diameter must be 4”. The appliance should be
located as close to the point of termination as possible (see
Fig. 5 for locating the terminator). The vent system should
be as straight and short as possible. The vent pipe must be
4” single wall stainless steel (AL29-4C) or galvanized steel
pipe of 26 minimum gauge. Maximum vent length is 15
feet (4.6 m) with two 90-degree elbows. Subtract 5 feet
from the total vent length for each additional 90-degree
elbow used. No more than four 90-degree elbows may be
used. Any short vertical portion of vent pipe used in the
vent system shall be considered part of the allowable 15
feet (4.6 m) maximum run. Support the vent run at 4 foot
intervals with overhead hangers. Horizontal sections of vent
must rise ¼” for every foot of horizontal length. Any vent
section greater than 45 degrees is considered an elbow.
Note: Single wall pipe should not be used in concealed,
unoccupied or unheated locations. Listed thimbles or collars
are necessary to pass through wall partitions. If the vent
system passes through combustible areas where the vent
clearance requirements cannot be maintained, it is
permissible to chase straight sections of sealed 4 inch single
wall vent through 5 inch (or greater) Type-B vent. The
distance to combustibles using this chase technique is 1
inch. Note: Type-B vent should never be used as the actual
vent system for the 125FX, as it is not gas tight.
Freeze Warning:
As mentioned on Page 5, negative air pressure in cold
climates will cause a reverse airflow in the vent system that
can freeze and damage the Aquastar heat exchanger when
not in use. To prevent this the FXHOOD horizontal vent
terminator, which was supplied separately with the water
heater, needs to be installed on the end of the horizontal
vent run (see page 8). The FXHOOD is a CSA approved
vent terminator for the Aquastar 125FX and has a built in
back draft flapper.
Flue Gas Sensor:
The 125FX is equipped with a Flue Gas Sensor; it’s mounted
on the left side of the draft diverter (Flue Gas Sensor - #33
on page 20). Before leaving the installation site verify proper
Flue Gas Sensor operation by temporarily blocking
termination outlet. Once blocked then operate the heater,
the unit should shut down within 1-3 minutes when the flue
gases are blocked. You must reset the electrical power to
the heater after this safety test has been conducted,
otherwise the unit will not operate.
Venting Material
Exhaust vent
Exhaust vent maximum
Vent pipe within an
unenclosed space
Vent pipe within an
enclosed space
Single wall stainless
steel (AL29-4C)
sealed vent
4 inch
15 feet (4.6 m) with two
elbows. Less 5 feet for
each additional elbow.
*See manufacturer's
*See manufacturer's
Single wall galvanized
vent pipe (min. 26
gauge and sealed
with high temperature
4 inch
15 feet (4.6 m) with two
elbows. Less 5 feet for
each additional elbow.
from venting
The flue gas exhaust temperature on the 125 FX is 356°F (180°C)
*Stainless steel (AL29-4C) vent pipe manufacturer's are Z-Flex, Protech and Heat Fab. The manufacturer's specified clearances
are identified on the venting material. NOTE: clearance distances are variable depending if the vent pipe is installed in an
enclosed or unenclosed space, the exhaust flue gas temperature and the orientation of the vent pipe.