MG2S Installation Manual

10
Existing Installations
When an existing furnace is removed from a vent system
serving other appliances, the existing vent system may
not be sized properly to vent the remaining appliances
(example: water heater). An improperly sized venting
system can result in the formation of condensate, leakage,
or spillage. The existing vent system should be checked
to make sure it is in compliance with NFGC and must be
brought into compliance before installing the furnace.
NOTE: If replacing an existing furnace, it is possible you
will encounter an existing plastic venting system that is
subject to a Consumer Product Safety Commission recall.
The pipes involved in the recall are High Temperature
Plastic Vent (HTPV). If your venting system contains
these pipes DO NOT reuse this venting system! This
recall does not apply to other plastic vent pipes, such
as white PVC or CPVC. Check for details on the CPSC
website or call their toll-free number [phone].
Ventilaire III or IV Air Quality Package
The Ventilaire air quality accessory packages are available
to meet the ventilation requirements as outlined in H.U.D.
Standard Part 3280.103 (b) (2). These packages introduce
outdoor air into the living space during furnace blower
operation. The VentilAire IV also serves to exhaust moist
and/or hot air from the attic space. See Figure 5 for typical
installation. Complete installation instructions are supplied
with each air quality package.
VentilAire III
VentilAire IV
Figure 5. VentilAire III & IV
Vent Freezing Protection
CAUTION:
When the vent pipe is exposed to temperatures
below freezing (i.e., when it passes through
unheated spaces, chimneys, etc.) the pipe
must be insulated with 1/2 inch thick sponge
rubber insulation, Armaflex-type insulation or
equivalent. Insulating pipe is important to avoid
condensate icing.
• Table 3 lists the maximum length of flue pipe that can
travel through an unconditioned space or an exterior
space. The total vent length must not exceed the
lengths noted in the table. For Canadian installations,
please refer to the Canadian Installation Code (CAN/
CGA-B149.1 or 2) and/or local codes.
• For extremely cold climates or for conditions of short
furnace cycles (i.e. set back thermostat conditions)
the last 18 inches of vent pipe can be reduced. It is
acceptable to reduce from 3” to 2-1/2” or, 3” to 2” if the
total vent length is at least 15 feet in length, and the
vent length is within the parameters specified in Table
2, (page 8). The restriction should be counted as 3
equivalent feet. Smaller vent pipes are less susceptible
to freezing, but must not be excessively restrictive. .
• To prevent debris or creatures from entering the
combustion system, a protective screen may be
installed over the combustion air intake opening. The
screens hole size must be large enough to prevent air
restriction.
Winter Design
Temperature
Maximum Flue Pipe Length (FEET)
in Unconditioned & Exterior Spaces
Without Insulation With Insulation*
20 45 60
0 20 60
-20 10 60
*NOTE: Insulation thickness greater than 3/8 inch, based on an
R value of 3.5 (ft x F x hr) / (BTU x in.)
Table 3. Vent Protection