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Provide duct transitions, as required, to smoothly transition airflow
from the return duct system to the filter (or IAQ device) to the
furnace when the dimensions of the ductwork or furnace return air
opening do not match the required filter or IAQ device dimensions.
See the instructions supplied with factory- -accessory duct adapters.
There are no provisions for an internal filter in these furnaces. An
external filter rack is required and is purchased separately. A field
supplied accessory air cleaner may also be used in place of the filter
rack.
For upflow applications, the filter can be installed on either side of
the furnace, the bottom of the furnace or any combination of side
and bottom of the furnace. (See Fig. 19 and 26.)
For downflow applications, the filter rack (or field supplied
accessory air cleaner) must only be connected to the bottom
opening on the furnace. (See Fig. 19 and 27.)
Table 5 – Filter Media Pressure Drop (Clean) Versus Airflow - - In. W.C. (Pa)
14 x 25 Filter
Factory-Accessory
(356 x 635 mm)
Washable
CFM
L/s
(1-in. / 2.5 cm)
600
(283)
0.04
800
(378)
0.06
1000
(472)
0.07
1200
(566)
0.08
16 x 25 Filter
Factory-Accessory
(406 x 635 mm)
Washable
CFM
L/s
(1-in. / 2.5 cm)
600
(283)
0.04
800
(378)
0.05
1000
(472)
0.06
1200
(566)
0.07
1400
(661)
0.08
1600
(755)
0.09
1800
(850)
0.10
20 x 25 Filter
Factory-Accessory
(508 x 635 mm)
Washable
CFM
(L/s)
(1-in. / 2.5 cm)
800
(378)
0.04
1000
(472)
0.05
1200
(566)
0.06
1400
(661)
0.07
1600
(755)
0.08
1800
(850)
0.08
2000
(944)
0.09
2200
(1038)
0.09
25 x 25 Filter
Factory-Accessory
(635 x 635 mm)
Washable
CFM
L/s
(1-in. / 2.5 cm)
800
(378)
0.03
1000
(472)
0.04
1200
(566)
0.05
1400
(661)
0.06
1600
(755)
0.06
1800
(850)
0.07
2000
(944)
0.08
2200
(1038)
0.08
If the filter size that you are looking for is not contained in Table 5, refer to Table 6 for a comparison of Pressure Drop (initial/clean resistance
to airflow) versus Face Velocity for a variety of filter media types.
The following equations relate Face Velocity (FPM), Filter Area and Airflow (CFM):
Filter Face Velocity = Airflow / Filter Area
Minimum Filter Area = Rated System Airflow / Maximum Filter Face Velocity
Factory-Accessory
Media*
(4-in. / 10 cm)
(12)
0.05
(12)
(15)
0.07
(19)
(18)
0.10
(27)
(20)
0.14
(36)
Factory-Accessory
Media*
(4-in. / 10 cm)
(10)
0.05
(13)
(13)
0.07
(18)
(16)
0.11
(28)
(18)
0.15
(37)
(21)
0.19
(48)
(23)
0.24
(60)
(25)
-
-
Factory-Accessory
Media*
(4-in. / 10 cm)
(11)
0.05
(12)
(13)
0.07
(18)
(15)
0.09
(22)
(17)
0.12
(31)
(19)
0.15
(38)
(21)
0.18
(47)
(23)
0.22
(56)
(24)
0.26
(66)
Factory-Accessory
Media*
(4-in. / 10 cm)
(9)
0.03
(8)
(11)
0.05
(12)
(13)
0.07
(17)
(15)
0.09
(23)
(16)
0.12
(31)
(18)
0.14
(35)
(19)
0.16
(41)
(21)
0.19
(49)
For horizontal applications, the filter rack (or field supplied
accessory air cleaner) can be connected to the bottom opening on
the furnace. For side return use in the horizontal position, refer to
Fig. 28. If both side and bottom openings are used in Fig. 28, each
opening used will require a filter.
A filter rack or any field supplied accessory air cleaner can also be
installed in the common return duct prior to entering the return air
opening in any orientation.
Refer to the instructions supplied with the Filter Rack or accessory
air filter for additional assembly and installation
See Table 7 for recommended filter size details.
Representative After-Market Filter Media*
Fiberglass*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.07
(17)
0.10
(26)
0.10
(25)
0.15
(39)
0.13
(34)
0.21
(52)
0.17
(43)
0.27
(68)
Representative After-Market Filter Media*
Fiberglass*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.06
(15)
0.09
(22)
0.08
(21)
0.13
(32)
0.11
(28)
0.17
(43)
0.14
(36)
0.22
(56)
0.18
(45)
0.28
(70)
0.21
(54)
-
0.26
(64)
-
Representative After-Market Filter Media*
Fiberglass*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.06
(16)
0.09
(24)
0.08
(21)
0.13
(32)
0.11
(27)
0.16
(41)
0.13
(33)
0.20
(51)
0.16
(40)
0.24
(61)
0.18
(47)
0.29
(73)
0.21
(54)
-
0.25
(62)
-
Representative After-Market Filter Media*
Fiberglass*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.05
(12)
0.07
(18)
0.06
(16)
0.09
(24)
0.08
(20)
0.12
(31)
0.10
(24)
0.15
(38)
0.11
(29)
0.18
(45)
0.13
(34)
0.21
(53)
0.16
(39)
0.24
(61)
0.18
(45)
0.28
(70)
23
options.
Pleated*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.24
(60)
0.16
0.34
(85)
0.23
-
-
0.32
-
-
-
Pleated*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.20
(51)
0.13
0.29
(72)
0.20
-
-
0.27
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Pleated*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.22
(55)
0.15
0.29
(72)
0.20
-
-
0.25
-
-
0.31
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Pleated*
(1-in. / 2.5 cm)
(2-in. / 5 cm)
0.17
(43)
0.11
0.22
(55)
0.15
0.27
(68)
0.18
-
-
0.23
-
-
0.28
-
-
-
-
-
-
-
-
-
(40)
(59)
(81)
-
(34)
(49)
(67)
-
-
-
-
(37)
(49)
(63)
(79)
-
-
-
-
(28)
(37)
(47)
(58)
(69)
-
-
-
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