270844-YTG-A-0407
Unitary Products Group
5
RETURN AIR AND FILTERS
The return air ducts to the furnace must have a total cross
sectional area of not less than two square inches per 1000
BTUH of furnace input rating for heating operation.
If air con-
ditioning is to be installed with the furnace, or if it may be
added at a later time, larger return air ducts may be
required, depending on the capacity of the air condi-
tioner and the airflow required.
FILTER PERFORMANCE
The airflow capacity data published in the “Blower Perfor-
mance” table listed above represents blower performance
WITHOUT filters. To determine the approximate blower per-
formance of the system, apply the filter drop value for the fil-
ter being used or select an appropriate value from the “Filter
Performance” table shown.
The filter pressure drop values in the “Filter Performance”
table shown are typical values for the type of filter listed and
should only be used as a guideline. Actual pressure drop rat-
ings for each filter type vary between filter manufacturers.
BOTTOM/END RETURN
G8C05012(MU,MD)B12
1
B
High
1419
1357
1297
1212
1131
1050
942
846
Med
1221
1185
1145
1092
1036
961
879
780
Low
920
902
883
860
818
761
711
639
G8C07512(MU,MD)B12
1
B
High
1552
1491
1420
1348
1271
1185
1080
970
Med
1229
1237
1198
1164
1105
1039
956
861
Low
889
892
879
866
846
807
760
689
G8C07516(MU,MD)C12
1
C
High
1946
1862
1775
1620
1518
1409
1291
1160
Med
1683
1611
1551
1484
1388
1300
1190
1080
Low
1110
1138
1175
1190
1175
1126
1041
937
G8C10016(MU,MD)C12
1
C
High
1997
1920
1822
1723
1620
1500
1355
1211
Med
1728
1679
1635
1556
1465
1359
1249
1117
Low
1131
1156
1181
1190
1171
1126
1049
926
G8C10020(MU,MD)D11
2
D
High
2327
2232
2121
1999
1888
1763
1628
1473
Med-High
2050
1967
1868
1757
1658
1525
1403
1260
Med-Low
1911
1839
1758
1675
1593
1468
1340
1189
High
1780
1712
1642
1566
1465
1366
1249
1094
G8C12520(MU,MD)D11
2
D
High
2397
2304
2192
2063
1955
1822
1678
1521
Med-High
2151
2063
1977
1881
1774
1652
1528
1377
Med-Low
1972
1906
1838
1748
1660
1551
1419
1282
Low
1845
1794
1721
1646
1559
1451
1344
1208
G8C15020UHD11
2
D
High
2488
2389
2276
2151
2024
1883
1730
1577
Med-High
2164
2084
2024
1920
1816
1692
1558
1395
Med-Low
1998
1934
1868
1773
1673
1567
1445
1294
Low
1843
1793
1728
1653
1553
1453
1328
1192
1. Return air is through side opposite motor (left side) for one side return (worst case).
2. Airflows above 1800 CFM (50.97 m
3
/min) require either return from two sides or one side plus bottom
3. Airflows expressed in standard cubic feet per minute (CFM) and in cubic meters per minute (m
3
/min).
BLOWER PERFORMANCE (CONTINUED)
BTU/H (kW)
Input
Cabinet
Size
Speed
Tap
External Static Pressure, Inches WC - CFM
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
For applications requiring more than 1800 CFM, it
is required to use the bottom return, both side
returns or one side plus the bottom return.
• Single side return is not approved on 5 Ton mod-
els.
• 18” minimum height for return air box for bottom
return only on Heating only applications with fur-
nace in the upflow configuration.
• 24” minimum height for return air box for bottom
return only on A/C applications with furnace in
the upflow configuration.
