27
AIR DUCTS
General Requirements
The duct system should be designed and sized according to
accepted national standards such as those published by: Air
Conditioning Contractors Association (ACCA), Sheet Metal and
Air Conditioning Contractors National Association (SMACNA) or
American Society of Heating, Refrigerating and Air Conditioning
Engineers (ASHRAE) or consult The Air Systems Design
Guidelines reference tables available from your local distributor.
The duct system should be sized to handle the required system
design CFM at the design external static pressure. The furnace
airflow rates are provided in Table 7--Air Delivery--CFM (With
Filter). When a furnace is installed so that the supply ducts carry air
circulated by the furnace to areas outside the space containing the
furnace, the return air shall also be handled by duct(s) sealed to the
furnace casing and terminating outside the space containing the
furnace.
Secure ductwork with proper fasteners for type of ductwork used.
Seal supply-- and return--duct connections to furnace with code
approved tape or duct sealer.
NOTE: Flexible connections should be used between ductwork
and furnace to prevent transmission of vibration.
Ductwork passing through unconditioned space should be
insulated to enhance system performance. When air conditioning is
used, a vapor barrier is recommended.
Maintain a 1--in. (25 mm) clearance from combustible materials to
supply air ductwork for a distance of 36--in. (914 mm) horizontally
from the furnace. See NFPA 90B or local code for further
requirements.
Ductwork Acoustical Treatment
NOTE: Metal duct systems that do not have a 90 degree elbow
and 10 ft. (3 M) of main duct to the first branch take--off may
require internal acoustical lining. As an alternative, fibrous
ductwork may be used if constructed and installed in accordance
with the latest edition of SMACNA construction standard on
fibrous glass ducts. Both acoustical lining and fibrous ductwork
shall comply with NFPA 90B as tested by UL Standard 181 for
Class 1 Rigid air ducts.
NOTE: For horizontal applications, the top most flange may be
bent past 90_ to allow the evaporator coil to hang on the flange
temporarily while the remaining attachment and sealing of the coil
are performed.
Table 7 – Air Delivery -- CFM (With Filter)
INPUT
BTUH
RETURN-AIR
SUPPLY
SPEED
EXTERNAL STATIC PRESSURE (IN. W.C.)
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
40000 SIDE/BOTTOM
5(Gry) 1120 1080 1030 980 925 875 820 760 690 630
4(Yel) 880 845 810 780 740 710 680 640 615 570
3(Blu) 695 665 620 575 535 495 455 420 370 280
2(Org) 640 595 540 495 460 420 370 310 260 230
1(Red) 570 525 475 425 385 330 255 220 - -
60000 SIDE/BOTTOM
5(Gry) 1720 1670 1620 1565 1505 1440 1375 1295 1220 1135
4(Yel) 1325 1285 1255 1220 1185 1145 1115 1075 1040 1000
3(Blu) 1010 970 925 875 835 785 745 690 660 620
2(Org) 1160 1115 1080 1045 1000 960 920 875 840 785
1(Red) 785 715 655 595 530 490 435 385 340 285
80000 SIDE/BOTTOM
5(Gry) 1810 1770 1720 1665 1610 1540 1475 1400 1315 1235
4(Yel) 1535 1500 1475 1435 1405 1370 1340 1310 1245 1160
3(Blu) 1380 1340 1305 1270 1240 1200 1165 1130 1090 1050
2(Org) 1180 1130 1095 1060 1015 975 935 895 850 800
1(Red) 1100 1045 1010 970 920 885 845 790 745 690
100000 SIDE/BOTTOM
5(Gry) 2040 1970 1885 1795 1720 1635 1540 1450 1360 1230
4(Yel) 1550 1505 1460 1415 1365 1325 1280 1230 1180 1135
3(Blu) 1780 1730 1690 1645 1610 1555 1481 1400 1310 1210
2(Org) 1345 1295 1250 1195 1155 1105 1055 1000 955 915
1(Red) 1390 1350 1295 1260 1200 1160 1105 1050 1010 965
120000
BOTTOM
OR
TWO SIDES
5(Gry) 2275 2230 2185 2130 2055 1950 1825 1710 1610 1500
4(Yel) 1875 1820 1770 1720 1660 1600 1550 1505 1450 1390
3(Blu) 2170 2125 2075 2025 1975 1900 1790 1695 1590 1470
2(Org) 1475 1420 1350 1280 1215 1165 1105 1050 995 930
1(Red) 1625 1565 1505 1445 1385 1325 1275 1225 1170 1130
*A filter is required for each return ---air inlet. Airflow performance included 3/4---in. (19 mm) washable filter media such as contained in factory --- a u t h o r i z e d
accessory filter rack. To determine airflow performance without this filter, assume an additional 0.1 in. W.C. available external static pressure.
--- Indicates unstable operating conditions.
59SP5A
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