MG3P Installation Manual

11
of the furnace combustion system. See list of substances on
page 4.
• Route piping as direct as possible between the furnace and
the outdoors. Horizontal piping from inducer to the flue pipe
must be sloped 1/4” per foot to ensure condensate flows
towards the drain tee or PVC trap. Longer vent runs require
larger pipe diameters. Refer to the Inducer & Venting Options
section on page 18 for additional information..
• The combustion air intake and the vent exhaust must be
located in the same atmospheric pressure zone. This means
both pipes must exit the building through the same portion of
exterior wall or roof as shown in Figure 7 (page 10), Figure
8, Figure 9 (page 10), & Figure 10.
• Piping must be mechanically supported so that its weight
does not bear on the furnace. Supports must be at intervals
no greater than 5 ft. Supports may be at shorter intervals if
necessary to ensure that there are no sagging sections that
can trap condensate.
Outdoor Terminations - Horizontal Venting
Vent and combustion air intake terminations shall be installed
as depicted in Figure 7, Figure 8, and in accordance with these
instructions:
• Vent termination clearances must be consistent with the NFGC,
ANSI 2223.1/NFPA 54 and/or the CSA B149.1, Natural Gas
and Propane Installation Code.
• All minimum clearances must be maintained to protect building
materials from degradation by flue gases as shown in Figure
8.
• Vent and combustion air intake terminations must be located
to ensure proper furnace operation and conformance to
applicable codes. The minimum distance from any door, open
window, or air gravity inlet is 1ft. below, 1ft. horizontally, or
1ft. above. In Canada, CSA B149.1 takes precedence over
these instructions. Table 20 (page 49) lists the necessary
distances from the vent termination to windows and building
air intakes.
• The vent termination shall be located at least 4 ft. horizontally
from any electric meter, gas meter, regulator and any relief
equipment. These distances apply ONLY to U.S. installations.
In Canada, the Canadian Fuel Gas Code takes precedence
over these instructions.
• Do not install the vent terminal such that exhaust is directed
into window wells, stairwells, under decks or into alcoves or
similar recessed areas, and do not terminate above any public
walkways.
• If venting horizontally, a side wall vent kit is available according
to the pipe diameter size of the installation. 2 inch and 3 inch
kits are available. Refer to the technical sales literature for
part numbers. Please follow the instructions provided with
the kit.
• Concentric vent kits are available for both 2” and 3” applications.
Each size has one that meets UL 1738 and one that meets ULC
S636. Refer to the technical sales literature for kit numbers.
• When the vent pipe must exit an exterior wall close to the
grade or expected snow level where it is not possible to obtain
clearances shown in Figure 7, a riser may be provided as
shown in Figure 9 (page 10). Insulation is required to prevent
freezing of this section of pipe. For vent freezing protection,
see page 12.
WARNING:
The combustion air vent and exhaust vent must
be configured as shown in Figure 9. Improper vent
terminations can cause the recirculation of flue
gases which may result in furnace vibration. In
severe cases, the furnace will cycle, due to the
intermittent contact between the flame and the
flame sensor. If you notice these oscillations
occurring, check the vent configuration to make
sure the exhaust vent does not have a 90 degree
termination.
• For optimal performance, vent the furnace through a wall that
experiences the least exposure to winter winds.
• Termination kits consist of two face plates and an insulating
gasket to seal the exterior surface.
• The hole in the wall must be sized closely to the diameter of
the pipe.
• The pipe that penetrates the wall should be long enough that
it can be held in place by standard close fitting couplings.
• Face plates are secured to both sides of the wall by the
couplings, and the gasket is retained against the wall by the
exterior face plate.
• Face plates must be fastened to the wall. Exterior face plates
must be flashed to prevent water infiltration.
If termination kits are not used, these requirements must
be followed:
• The hole size cut through the exterior wall is smaller than the
outside diameter of the couplings.
• The vent pipe extends through the wall approximately 1" and
the gap between the wall and pipe is sealed.
• Couplings are applied to the vent pipe on the interior and
exterior sides of the wall. NOTE: This insures the pipe can
not be pushed or pulled through the wall.
• The combustion air inlet pipe must have a 90 degree termination
elbow, and pointed downwards as shown in Figure 7 (page
10).
Outdoor Terminations - Vertical Venting
Termination spacing requirements from the roof and from each
other are shown in Figure 10.
• The roof penetration must be properly flashed and waterproofed
with a plumbing roof boot or equivalent flashing.
• The combustion air intake must be provided with an elbow
opening downward.
Vent and combustion air piping may be installed in an existing
chimney which is not in use provided that:
• Both the exhaust vent and air intake run the length of the
chimney.
• The top of the chimney is sealed and weatherproofed.
• The termination clearances shown in Figure 10 are maintained.
• No other gas fired or fuel-burning equipment is vented through
the chimney.
Figure 10. Vertical Vent Termination
Combustion Air
Exhaust Vent
12” Above Maximum
Expected Snow Level
(Both pipes)
Elbows on the combustion air
inlet must be positioned pointing
away from the exhaust vent.
8" Min.
36" Max.
Plumbing Vent Roof Boot
(Both Pipes)