Mighty Therm Lo-Nox
Page 5
2.2.1.b Forced-Air Ventilation
In the United States: any equipment which
exhausts air from the heater 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 heater room. Additional
air must be supplied to compensate for such exhaust.
The information in Table 2 is not applicable in
installations where exhaust fans or blowers of any
type are used. Such installations must be designed by
qualified engineers.
In Canada: follow Canadian standard, CAN/
CGA B-149 or local codes.
If a blower or fan is used to supply air to the
heater room, the installer should make sure it does not
create drafts which could cause nuisance shutdowns. If
a blower is necessary to provide adequate combustion
air to the heater, a suitable switch or interlock must be
wired into the heater control circuit to prevent the
heater from firing unless the blower is operating.
The heater must be completely isolated and
protected from any source of corrosive chemical fumes
such as trichlorethylene, perchloroethylene, chlorine, etc.
2.2.2 Venting
1.
Laars heaters have built-in draft diverters for
natural draft operation and must not be
connected to any portion of a mechanical draft
system under positive pressure. The flue outlet
must be connected to a clear, unobstructed vent
of adequate capacity ending above the highest
point of the building with an approved vent cap.
The venting system should be installed according
to Category 1, Natural Draft per the latest edition
of ANSI Z223.1 and/or, in Canada, CAN/CGA
B-149 and any local codes having jurisdiction.
2.
Do not weld or fasten the vent pipe to the boiler
drafthood. The weight of the stack must not rest
on the heater. The drafthood and heater top must
be easily removable for normal heater service
and inspection.
IMPORTANT NOTE: Do not use sheet metal
screws at the snap lock joints of Type B gas vents.
3.
Avoid using long horizontal runs of the vent
pipe, and too many 90° elbows, reductions or
restrictions. Horizontal runs should have at least
a 1/4" (6mm) rise per foot in the direction of
flow. A vent connector should be supported for
the design and weight of the material used to
maintain clearances and prevent physical damage
and separation of joints.
4.
Avoid terminating heater vents near air
conditioning or air supply fans. The fans can
pick up exhausted flue products from the heater
and return them inside the building creating a
possible health hazard. A minimum of 4 feet
(1.2m) horizontal distance must be maintained
from electrical meters, gas meters, and relief
equipment.
5.
Always use double-wall or insulated vent pipe
(Type B or equivalent). In cold weather,
uninsulated outside vents can chill the rising flue
products blocking the natural draft action of the
venting systems. This can create a health hazard
by spilling flue products in the heater room.
6.
Avoid oversized vent piping or extremely long
runs of 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. Longer
total lengths shown in venting tables are based
on maximum capacity, not condensation factors.
7.
When the installation of a draft fan is necessary
in connecting a venting system to a Laars heater,
the installation should be engineered by
competent personnel following good engineering
practices. The draft fan supplier should be
consulted for correct size. The installation should
be in accordance with the latest edition of ANSI
Figure 4. Typical Heater Installation on Concrete Slab.
Heater
Each Opening*
Size
square inches
square cm
500
125
806.5
715
179
1154.9
1010
253
1632.4
1430
358
2309.8
1825
457
2948.6
* Net Free Area.
Check with louver manufacturers for net free area of louvers.
Correct for screen resistance to the net free area if a screen is
installed. Check all local codes applicable to combustion air.
Area indicated is for one of two openings: one at floor level
and one at the ceiling, so the total net free area could be
double the figures indicated. For special conditions refer to the
latest edition of ANSI Z223.1.
Consult factory if openings do not communicate directly
through the walls with the outdoors.
Table 2. Minimum Recommended Air Supply to Heater.
