Page 38
NOTE − The flue collar on all models is sized to accommo-
date 2" Schedule 40 flue pipe. When vent pipe which is
larger than 2" must be used in an upflow application, a 2"
elbow must be applied at the flue collar in order to proper-
ly transition to the larger diameter flue pipe. This elbow
must be added to the elbow count used to determine ac-
ceptable vent lengths. Assign an equivalent feet value to
this elbow according to the larger size pipe being used.
Contact the Application Department for more information
concerning sizing of vent systems which include multiple
pipe sizes.
Use the following steps to correctly size vent pipe diameter.
Refer to Vent Pipe Size Determination Worksheet
Figure 16.
1 − Determine the vent termination and its corresponding
equivalent feet value according to table 34.
2 − Determine the number of 90° elbows required for both
indoor and outdoor (e.g. snow riser) use. Calculate the
corresponding equivalent feet of vent pipe.
3 − Determine the number of 45° elbows required for both
indoor and outdoor use. Calculate the corresponding
equivalent feet of vent pipe.
4 − Determine the length of straight pipe required.
5 − Add the total equivalent feet calculated in steps 1
through 4 and compare that length to the maximum
values given in table 36 for the proposed vent pipe di-
ameter. If the total equivalent length required exceeds
the maximum equivalent length listed in the appropri-
ate table, evaluate the next larger size pipe.
IMPORTANT
Do not use screens or perforated metal in exhaust or
intake terminations. Doing so will cause freeze−ups
and may block the terminations.
TABLE 35
MINIMUM VENT PIPE LENGTHS
G71MPP
MODEL
MIN. EQUIV.
VENT LENGTH
EXAMPLE
070, 090
15 ft.*
5 ft. plus 2 elbows of 2", 2−1/2", 3"
or 4" diameter pipe
110**
5 ft. plus 2 elbows of 2−1/2" 3" or 4"
diameter pipe
135***
5 ft. plus 2 elbows of 3" or 4"
diameter pipe
*Any approved termination may be added to the minimum equivalent length
listed.
**G71MPP−60C−110 must have 90° street ell (supplied) installed directly into
unit flue collar.
***G71MPP−60D−135 must have 3" to 2" reducing ell (supplied) installed direct-
ly into unit flue collar.
TABLE 36
MAXIMUM VENT PIPE LENGTHS
ALTITUDE
G71MPP
MODEL
MAXIMUM EQUIVALENT VENT
LENGTH FEET
2"
PIPE
2−1/2"
PIPE
3"
PIPE
4"
PIPE
0 − 7500
(0 − 2286 m)
070
75
135
150
250
090
50
100
125
225
110*
20
60
125
200
135**
n/a
n/a
125
180
7501 − 10000
(2287 − 3048 m)
070
60
125
150
250
090
25
60
125
225
110*
n/a
40
90
200
135**
n/a
n/a
70
180
n/a −− Not allowed.
*G71MPP−60C−110 must have 90° street ell (supplied) installed directly into
unit flue collar.
**G71MPP−60D−135 must have 3" to 2" reducing ell (supplied) installed directly
into unit flue collar.
NOTE − Elbows and pipe required for vent terminations must be added
when calculating equivalent vent length.
B−Joint Cementing Procedure
All cementing of joints should be done according to the
specifications outlined in ASTM D 2855.
WARNING
DANGER OF EXPLOSION!
Fumes from PVC glue may ignite during system
check. Allow fumes to dissipate for at least 5 minutes
before placing unit into operation.
1 − Measure and cut vent pipe to desired length.
2 − Debur and chamfer end of pipe, removing any ridges
or rough edges. If end is not chamfered, edge of pipe
may remove cement from fitting socket and result in a
leaking joint.
3 − Clean and dry surfaces to be joined.
4 − Test fit joint and mark depth of fitting on outside of pipe.
5 − Uniformly apply liberal coat of PVC primer for PVC or
use a clean dry cloth for ABS to clean inside socket
surface of fitting and male end of pipe to depth of fitting
socket.
NOTE − Furnace flue collar and air inlet fitting are both
ABS pipe. Use transition solvent cement when joining
ABS pipe to PVC pipe.
6 − Promptly apply solvent cement to end of pipe and in-
side socket surface of fitting. Cement should be ap-
plied lightly but uniformly to inside of socket. Take
care to keep excess cement out of socket. Apply sec-
ond coat to end of pipe.
NOTE − Time is critical at this stage. Do not allow prim-
er to dry before applying cement.
