Midco G69B - Manual (Page 5)

-5-
FIGURE 8 Firing Door Installation in Three Pass Boiler
As an alternate, the burner mounting plate can be
extended externally to locate the nozzle face and
refractory wholly within the door opening. Seal carefully to
prevent flue products from entering the boiler room.
In double door boilers it is recommended that the openings
be enlarged to a single opening by removing the center
post so that the burner can fire in the center. If a pressure
part of the boiler must be cut away, be sure to make
modifications in accordance with your local code covering
boiler repairs.
Since firing door installations will generally leave no
openings for flame observation, a peep sight must be
installed in the burner mounting plate.
IV CHIMNEY, VENT CONNECTOR, AND
DRAFT CONTROL
WARNING: The chimney shall be inspected for
unsafe conditions such as deteriorated masonry and
excessive soot or other blockage or potential
blockage. Installation must conform with local codes
or in the absence of local codes with NFPA, ANSI
Z223.1-latest edition.
WARNING: No movable vent connector damper is
permitted on any gas conversion installation. The
chimney should be inspected for unsafe conditions
such as deteriorated masonry and excessive soot or
other blockage or potential blockage. Check your local
authorities for regulations covering barometric draft
regulators on gas equipment.
WARNING: The vent connector shall not be
connected to a chimney already venting solid fuel
burning equipment, an incinerator or an open fire
place.
The UNIPOWER burner does not depend on chimney
draft. Combustion air is supplied by the forced air blower,
which is sufficient to supply adequate air for any normal
boiler. This reduces the function of the chimney to removal
of flue products from the boiler. A chimney height of 15'
above the boiler flue outlet will generally prove ample if the
recommended, or larger, vent connector and chimney
diameters are used. The chimney must of course extend
several feet over the roof of the building, or adjacent
buildings. Vent connector material should be 24 gauge or
heavier steel, galvanized to resist corrosion. The horizontal
run of vent connector should be pitched upward from the
appliance flue outlet at least 1/4" to the foot. Avoid excess
elbows or other constructional features that would create
excessive resistance to flow of flue products. Fasten joints
with sheet metal screws to prevent sagging. The vent
connector should be maintained at least 6" from
combustible building materials; more if it is uninsulated.
Where it passes through partitions constructed of
combustible materials a ventilated thimble should be used.
Refer to your local building codes. The vent connector
should be firmly cemented into the chimney but must not
extend beyond the inner face. Where two or more
appliances use the same chimney, be sure not to enter the
chimney with both flue pipes at the same level.
Do not arbitrarily reduce the vent connector size, since a
boiler back pressure can build up, leading to possible
leakage of flue products into the boiler room.
Chimney construction can be either of brick, preferably tile
lined, or of steel. Joints in the chimney should be smooth
and leak free to prevent uncontrollable air infiltration. They
should be made so that condensation, if any, will not
collect in the joints or leak to the outside.
If the vent connector must be extra long, the area of the
pipe and chimney should be increased, or the chimney
height must be increased, or both. Never allow the
horizontal length of the vent connector to exceed the
height of the chimney.
Two kinds of draft control are acceptable; an A.G.A. type
draft hood as illustrated in Figure 9, or a barometric
damper as shown in Figure 10. Use of a draft hood is
usually limited to burners with lower range capacities,
while a barometric draft control is suitable for all
capacities. Application should depend on the requirements
of the installation.