Venting; Standard Venting - A.O. Smith HW 300 Instruction Manual

STANDARD VENTING

Type B venting may be used with these boilers. All local utility
regulations on venting should be followed.
Vent sizing, installation and termination shall be in accordance with
the current edition of the National Fuel Gas Code, ANSI Z223.1, or
CAN/CSA B149.1, Installation Codes, or applicable provisions of the
local building codes.
Vent connectors serving appliances vented by natural draft shall
not be connected into any portion of mechanical draft systems
operating under positive pressure.
The minimum distance from adjacent public walkways, adjacent
buildings, openable windows and building openings shall not be
less than those values specified in the National Fuel Gas Code,
ANSI Z223.1 or CAN/CSA B149.1, Installation Codes;
DRAFT HOOD
The draft hood furnished with this boiler must be installed without
alteration. Provision must be made if the boiler is installed in
confined space or a small boiler room to accommodate draft
hood spillage and avoid risks described above. The upper air
opening called for in the AIR REQUIREMENTS section of this
manual is for this purpose.
VENT CONNECTION
Size and install proper size vent pipe. Do not reduce pipe size to
less than that of the draft hood outlet.
Horizontal runs of vent pipe shall be securely supported by
adequately placed (approximately every 4 feet or 1 meter),
noncombustible hangers and/or slip joints suitable for the weight
and design of the materials employed to prevent sagging and to
maintain a minimum upward slope of 1/4" (21 mm/m) per foot
from the boiler to the vent terminals, see Figure 15. Dampers
or other obstructions must not be installed in the vent. Be sure
that the vent pipe does not extend beyond the inside wall of the
chimney.

VENTING

FIGURE 15. VENT PIPE INSTALLATION
Where a continuous or intermittent back draft is found to exist the
cause must be determined and corrected. A special vent cap may
be required. If the back draft cannot be corrected by the normal
methods or if a suitable draft cannot be obtained, a blower type
flue gas exhauster may be employed to ensure proper venting
and correct combustion if permitted by local codes.
Vent connectors serving appliances vented by natural draft shall
not be connected into any portion of mechanical draft systems
operating under positive pressure.
CONNECTING BOILER TO A COMMON VENT
Do not connect the boiler to a common vent or chimney with solid
fuel burning equipment. This practice is prohibited by many local
building codes as is the practice of venting gas fired equipment
to the duct work of ventilation systems.
Where a separate vent connection is not available and the vent
pipe from the boiler must be connected to a common vent with oil
burning equipment, the vent pipe should enter the common vent
or chimney at a point ABOVE the flue pipe from the oil fired unit.
Where two or more appliances vent into a common vent connector
or manifold, the area of the common vent or vent connector
should at least equal the area of the largest vent connector plus
50% of the areas of the additional draft hood outlets.
When removing a boiler from a system with a common vent, use
the following steps:
Be sure the other appliances connected to the common vent are
not in operation.
Seal any unused openings in the common venting system.
Visually inspect the venting system for proper size and horizontal
pitch and determine there is no blockage or restriction, leakage,
corrosion and other deficiencies which could cause an unsafe
condition.
Insofar as is practical, close all building doors and windows and
all doors between the space in which the appliances remaining
connected to the common venting system are located and other
spaces of the building. Turn on clothes dryers and any appliance
not connected to the common venting system. Turn on any
exhaust fans, such as range hoods and bathroom exhausts, so
they will operate at maximum speed. Close fireplace dampers.
Place in operation the appliance being inspected. Follow the
lighting instructions. Adjust thermostat so appliance will operate
continuously.
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