Mini-Therm II Hydronic Boiler
Page 7
Outside Air Supply: When combustion air is
supplied directly through an outside wall, each opening
should have a minimum free area of one square inch per
4,000 BTU/h (1.2kW) input of the total input rating of
all appliances in the enclosed area.
Inside Air Supply: When combustion is
supplied from inside the building, each opening
should have a minimum free area of one square inch
per 1,000 BTU/h (0.3kW) input of the total input
rating of all appliances in the enclosed area. These
openings should never be less than 100 square inches
(645 sq. cm).
Note: In Canada, follow Canadian Standard,
CAN/CGA-B149.1, .2 or local codes.
Exhaust Fans or Vents: Any equipment which
exhausts air from the boiler room can deplete the
combustion air supply or reverse the natural draft
action of the venting system. This could cause flue
products to accumulate in the boiler room. Additional
air must be supplied to compensate for such exhaust.
The information in Table 5 is not applicable in
installations where exhaust fans or blowers of any
type are used. Such installations must be designed by
qualified engineers.
If a blower or fan is used to supply air to the
boiler room, the installer should make sure it does not
create drafts which could cause nuisance shutdowns of
the pilot. If a blower is necessary to provide adequate
combustion air to the boiler, a suitable switch or
equivalent must be wired into the boiler control circuit
to prevent the boiler from firing unless the blower is
operating.
The boiler must be completely isolated and
protected from any source of corrosive chemical
fumes such as those emitted by trichlorethylene,
perchlorethylene, chlorine, etc.
1H. Venting
The draft diverter outlet is to be connected to an
unobstructed vent pipe of the same or larger diameter,
terminating outside the building. The vent pipe must
have a listed vent cap, and extend at least two feet
above any object within a ten foot radius. All
connections should be made with rustproof sheet
metal screws.
IMPORTANT NOTE: Do not use sheet metal
screws at the snap lock joints of Type B gas vents.
Do not weld or fasten the vent pipe to the boiler
draft diverter. The weight of the stack must not rest on
the boiler. The draft diverter and boiler top must be
easily removable for normal boiler service and
inspection.
Avoid horizontal runs of the vent pipe, and 90°
elbows, reductions and restrictions. Horizontal runs
should have at least a 1/4" rise per foot (20mm per
meter) in the direction of flow. A vent connector shall
be supported for the design and weight of the material
employed to maintain clearances and prevent physical
damage and separation of joints.
Avoid terminating boiler vents near air
conditioning or air supply fans. The fans can pick up
exhaust flue products from the boiler and return them
inside the building, creating a possible health hazard.
Always use double-wall or insulated vent pipe
when used as a chimney (Type B or equivalent). In
cold weather, uninsulated outside vents can chill the
rising flue products, blocking the natural draft action
of the venting system. This can create a health hazard
by spilling flue products into the boiler room. Use
engineered venting tables acceptable to the authority
having jurisdiction to size the venting pipe or liner.
Avoid oversize vent piping or extremely long
runs of the pipe which may cause excessive cooling
and condensation.
Rule of Thumb: The total length of the vent,
including the connector and any offset, should not
exceed 15 feet (4.6m) for every inch (25mm) of vent
diameter (see Figure 5). Longer total lengths shown in
venting tables are based on maximum capacity, not
condensation factors.
Before connecting a vent connector to a
chimney, the chimney passageway shall be examined
to ascertain that it is clear and free of obstructions.
When inspection reveals that an existing chimney is
not safe for the intended application, it shall be rebuilt
to conform to nationally recognized standards (see
National Building Code or ANSI/NFPA 211), lined or
relined with a suitable liner, or replaced with a vent or
chimney suitable for the equipment to be attached.
Figure 5. Vent Pipe Sizing.
