035-17480-000 Rev. A (800)
18
Unitary Products Group
METHOD THREE: TWO PIPE SYSTEM USING
COMBUSTION AIR FROM A VENTILATED ATTIC
SPACE
This type installation requires two properly sized pipes. One
brings combustion air from a properly ventilated attic space
and a second pipe from the furnace vent connection (top right
of unit) exits to the outdoors.
COMBUSTION AIR INTAKE
Refer to Table 3 on page 12, for intake pipe sizing, allowable
length and elbow usage. Follow all notes, procedures and
required materials in the Two-Pipe Sealed Combustion sec-
tion (Method 1) when installing the combustion air pipe within
the unit and into the ventilated attic space.
COMBUSTION AIR TERMINATION
Refer to Figure 21 for required termination method and con-
figuration for the intake pipe. For attic termination, use two 90
elbows with the open end in a downward position. Be sure to
maintain 12" clearance above any insulation, flooring or other
material.
COMBUSTION AIR REQUIREMENTS
The ventilated attic space from which the combustion air is
taken must comply with the requirements shown on page
page 14 in this instruction or in Section 5.3, Air for Combus-
tion and Ventilation of the National Fuel Gas Code, ANSI
Z223.1 (latest edition).
VENT PIPE
For vent pipe sizing, allowable length and elbow usage, see
Table 5 on page 16. Follow all notes, installation procedures
and required materials in the “METHOD TWO ONE PIPE
SYSTEM”, on page 14 to install the vent pipe from the unit to
the outdoors.
VENT TERMINATION
The vent pipe termination must be installed within the allow-
able locations shown in FigureFigure 17 and Section 7.8 in
the National Fuel Gas Code, ANSI Z223.1 (current edition).
Follow all local agency and utility requirements if more restric-
tive than those shown. Vent termination must be as shown in
Figure 18 through Figure 20.
HORIZONTAL VENT APPLICATIONS
If installing a horizontal venting system through any uncondi-
tioned space such as an attic or crawl space, it is recom-
mended, but not required, that a vent drain be added to the
vent pipe to prevent the accumulation of excess condensate
in the inducer motor during operational cycles, refer to Fig-
ures 22.
In Canada, refer to CAN/CGA-B149.1 or .2 Installation Code
(latest edition - Venting Systems and Air Supply)
FIGURE 21 :
Attic Combustion Air
Termination
Be sure to instruct the owner not to block this
intake pipe.
1 2 " M I N I M U M B E T W E E N
B O T T O M O F E L B O W A N D
A N Y M A T E R I A L
1 2 "
M I N I M U M
In Canada, refer to CAN/CGA-B149.1 or .2 Installation Code
(latest edition - Venting Systems and Air Supply)
FIGURE 22 :
Horizontal Vent Drain -Upflow
Models P*XU / G9D-UP
NEUTRALS
EAC
COOL
HEAT
HUM
PARK
PARK
L1
XFMR
Y
W
R
G
C
3.00" Minimum
Loop Dia.
Attach This End
To Condensate
Drain System
