Mighty Therm
2
(200, 300, 400)
Page 9
2.1.2 Intake Combustion Air
The combustion air can be taken through the
wall, or through the roof. When taken from the wall, it
must be taken from out-of-doors by means of the Laars
horizontal wall terminal (
see Table 1
). When taken
from the roof, a field-supplied rain cap or an elbow
arrangement must be used to prevent entry of rain
water (
see Figure 2
).
Use single-wall galvanized pipe,
per Table
4,
for the combustion air intake (
see Table 1
for
appropriate size). Route the intake to the heater as
directly as possible. Seal all joints with tape. Provide
adequate hangers. The unit must not support the
weight of the combustion air intake pipe. Maximum
linear pipe length allowed is 50 feet (15.2m). Three
elbows have been calculated into the 50-foot (15.2m)
linear run. Subtract 10 allowable linear feet (3.0m) for
every additional elbow used (
see Table 1
). When fewer
than 3 elbows are used, the maximum linear pipe
length allowed is still 50 feet (15.2m).
Term
Description
Pipe
Single-wall galvanized steel pipe, 24 gauge
minimum (either insulated or non-insulated)
Joint Sealing Permanent duct tape or aluminum tape
Table 4. Required Combustion Air Piping Material.
The connection for the intake air pipe is on the
filter box. The Mighty Therm2 appliances may have
venting and combustion air ducting attached to the top
or the back. They are shipped with the connections
at the top. For attaching either or both pipes to the
back, the mounting flanges are reversible by removing
the mounting screws and orienting the flanges in the
desired position. Replace the screws after positioning
flanges. Run a bead of silicone around the collar and
slide the pipe over the collar. Secure with sheet metal
screws.
In addition to air needed for combustion, air
shall also be supplied for ventilation, including all air
required for comfort and proper working conditions
for personnel. The Mighty Therm2 loses less than 1
percent of its input rating to the room, but other heat
sources may be present.
2.2 Venting
2.2.1 Vent Categories
Depending upon desired Mighty Therm2 venting,
it may be considered a Category I or a Category III
appliance. In general, a vertical vent system will
be a Category I system. However, in rare instances,
a Mighty Therm2’s vertical vent system may be
considered Category III. In the U.S., the National Fuel
Gas Code (ANSI Z223.1), or in Canada the Natural
Gas and Propane Installation Code (CSA B149.1),
defines a Category I vent system, and includes rules
and tables to size these vent systems. If the Mighty
Therm2’s vertical vent system does not satisfy the
criteria for Category I venting, it must be vented as a
Category III system.
All Mighty Therm2 vent systems which
discharge horizontally (without the use of a power
venter) are considered Category III vent systems.
2.2.2 Category I Vent
When vented as a Category I appliance, the
vent system must conform to the National Fuel Gas
Code (ANSI Z223.1-Latest Edition) in the U.S., or in
Canada, to the Natural Gas and Propane Installation
Code (CSA B149.1 latest edition). The vent system
must be sized and installed for a Category I Fan-
Assisted Appliance.
If chimney height is greater than 25 feet, or
if multiple units are vented into the same vertical
vent, a barometric damper must be installed on each
appliance, such that the flue draft does not exceed
(negative) 0.1 in. w.c.
If using a power venter for any type of Category
I venting, the draft should be set between (negative)
0.01 and 0.05 in. w.c.
2.2.3 Common Venting Systems
Mighty Therm2 units are Category I fan-assisted
when vented vertically and adhering to all applicable
codes. Mighty Therm2 units are not allowed to be
vented into a common horizontal vent system, unless
a properly sized vent fan is used, and the common
vent system is properly designed by the vent fan
manufacturer or a qualified engineer. When common
venting Mighty Therm2 fan-assisted unit with other
appliances through one shared vertical duct called a
“common vent”, special care must be taken by the
installer to ensure safe operation. In the event that
the common vent is blocked, it is possible, especially
for fan-assisted devices, to vent backwards through
non-operating appliances sharing the vent, allowing
combustion products to infiltrate occupied spaces.
If the appliances are allowed to operate in this
condition, serious injury or death may occur.
