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AUTOMATIC VENT DAMPERS MUST BE
INSTALLED ONLY BY QUALIFIED SERVICE
TECHNICIANS. FAILURE TO PROPERLY
INSTALL A VENT DAMPER WILL CREATE A
SEVERE HAZARD.
PERFORMANCE TEST
The automatic vent damper must be tested after
installation to assure its proper and safe
operation.
AUTOMATIC VENT DAMPERS MUST BE IN
THE OPEN POSITION AT ANY TIME THE
APPLIANCE MAIN GAS VALVE IS ENERGIZED.
1.8.14 SIZING OF CHIMNEY AND VENT
IMPORTANT
The flue system calculations which follow in
Section 1.8.15 are applicable to double-wall or
insulated single wall breechings (vent connectors)
and stacks (vents). Do not apply these
calculations to uninsulated vent systems.
HIGH ALTITUDES
At altitudes of 2000 feet and higher, atmospheric
boilers must be derated. The amount of derate
required by the National Fuel Gas Code is 4% per
1000 feet above sea level. Boilers which are
shipped from the factory prepared for these
altitudes have the gas orifices properly sized for
this derate. The altitude and gas Btu content for
which the boilers have been constructed is listed
on the Equipment List/Submittal Data in the boiler
manual. The boilers will also be provided with a
label indicating that they have been prepared for
high altitude. If a boiler is to be installed at an
altitude other than that for which it was factory
built, orifices must be replaced to properly adjust
the gas input. Consult the factory or the local
Bryan Representative for the proper parts. For
the purpose of vent system sizing, assume full
input and determine sizing as if at sea level. The
derate factor of 4% per 1000 feet above sea
level accounts for the increased volume per
Btu/hr of flue products at high altitude.
INDUCED DRAFT FANS
Occasionally, the characteristics of an installation
are such that a natural draft vent system will not
suffice. In such cases, induced draft may be
used. The vent system is then sized with an
available "pumping" action equal to the total
theoretical draft plus the static pressure capability
of the induced draft fan. This will result in a
smaller diameter vent than for a natural draft
system. Sizing of induced draft fans should be
done using the recommendations of the fan
manufacturer and the ASHRAE Handbook.
FIG. 1.8.14: SUGGESTED APPLIANCE VENTING PROCEDURE
MULTIPLE APPLIANCE INSTALLATIONS
Bryan recommends that boilers and other gas
appliances be individually vented when possible.
See figure 1.8.14A. Individual venting provides
better draft control and fuel efficiency, and is less
likely to cause condensation in the system. When
individual venting is not possible, boilers may be
vented to a common breeching (vent connector).
See Fig. 1.8.14B for recommended design of
such a system. Note that connections of
individual boiler or appliance vents into the
common breeching should