Bosch 125B LPS - Manual (Page 9)

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Fig. 3 – Vent Adaptor for High Altitude Installations
5” X 6” ADAPTOR
USED ON HIGH ALTITUDE
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
appliances.
Run the unit for at least 10 minutes. Then hold an ordinary
mirror at the side above the front shell. Any flue gases
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 environment.
The mirror will remain clear with a properly functioning draft.
WARNING
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”S” instantaneous water heaters have
built-in draft diverters and are designed for indoor installation
only. The draft diverter outlet must be connected to an
unobstructed vent of the same size, or larger.
In Canada, CAN/CGA-B149 Installation Code for detailed
requirements
In U.S.A., ANSI Z223.1 - NFPA 54, National Fuel Gas
Code for detailed requirements.
The vent connection for the Aquastar 125BS is 5 inches.
However, for installations at high altitude (over 2000 feet
above sea level) a six inch vent is required. A 5” by 6” vent
adaptor must be affixed to the flue collar of the Aquastar
with at least two screws. See Fig. 3.
WARNING: Failure TO INCREASE THE VENT
SIZE TO SIX INCHES AND/or assure that the manifold
pressure is set to proper value listed for applications at high
altitudes will cause unsafe venting, asphyxiation, and will
void CSA Certification.