LAARS Mighty Therm2 MT2P (Sizes 500–2000 MBTU/h) - Install and Operating Manual - Manual (Page 7)

MT2P Pool Heater Page 7
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).
The connection for the intake air pipe is on
the filter box. MT2P appliances have venting and
combustion air ducting on the top.
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 MT2P 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 MT2P 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 MT2P’s vertical
vent system may be considered Category III. In the
U.S., the National Fuel Gas Code (American National
Standard Z223.1-Latest Edition), or in Canada the
CSA B149.1 (latest edition), defines a Category I vent
system, and includes rules and tables to size these vent
systems. If the MT2P’s vertical vent system does not
satisfy the criteria for Category I venting, it must be
vented as a Category III system.
All MT2P 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
(American National Standard Z223.1-Latest Edition) in
the U.S., or in Canada, to 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"
w.c.
If using a power venter for any type of Category I
venting, the draft should be set between (negative) 0.01
and 0.10" w.c.
2.2.3 Common Venting Systems
MT2P units are Category I fan-assisted when
vented vertically and adhering to all applicable codes.
MT2P 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 MT2P fan-assisted
heaters 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.
WARNING
Operation of appliances with a blocked common vent
may lead to serious injury or death. Safety devices
must be implemented to prevent blocked common
vent operation. If safe operation of all appliances
connected to a common vent cannot be assured,
including prevention of spillage of flue gasses
into living spaces, common venting should not be
applied, and appliances should each be vented
separately.
It is for this reason that, in addition to following
proper vent sizing, construction and safety requirements
from the National Fuel Gas Code, ANSI Z223.1 or in
TERM DESCRIPTION
Pipe Single-wall galvanized steel pipe, 24 gauge
minimum (either insulated or non-insulated)
Joint Permanent duct tape or aluminum tape
Sealing
Table 4. Required Combustion Air Piping Material. Figure 2. Combustion Air and Vent Through Roof.