PG92MSA: Installation, Start-up, Operating and Service and Maintenance Instructions
Manufacturer reserves the right to change, at any time, specifications and designs without notice and without obligations.
20
If the filter size that you are looking for is not contained in Table 7, refer to Table 8 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
Table 8 – Filter Media Pressure Drop (Clean) Versus Face Velocity- in. w.c. (Pa)
See Table 9 for filter size details.
Table 9 – Air Filter Selection and Duct Sizing - In. (mm) Air Filter Located in Filter Cabinet
20 x 25 Filter
(508 x 635 mm)
Factory-Accessory
Washable
Factory-Accessory
Media
*
Representative After-Market Filter Media
*
Fiberglass
*
Pleated
*
CFM (L/s) (1-in. / 2.5 cm) (4-in. / 10 cm) (1-in. / 2.5 cm) (2-in. / 5 cm) (1-in. / 2.5 cm) (2-in. / 5 cm)
800 (378) 0.04 (11) 0.05 (12) 0.06 (16) 0.09 (24) 0.22 (55) 0.15 (37)
1000 (472) 0.05 (13) 0.07 (18) 0.08 (21) 0.13 (32) 0.29 (72) 0.20 (49)
1200 (566) 0.06 (15) 0.09 (22) 0.11 (27) 0.16 (41) - - 0.25 (63)
1400 (661) 0.07 (17) 0.12 (31) 0.13 (33) 0.20 (51) - - 0.31 (79)
1600 (755) 0.08 (19) 0.15 (38) 0.16 (40) 0.24 (61) - - - -
1800 (850) 0.08 (21) 0.18 (47) 0.18 (47) 0.29 (73) - - - -
2000 (944) 0.09 (23) 0.22 (56) 0.21 (54) - - - - - -
2200 (1038) 0.09 (24) 0.26 (66) 0.25 (62) - - - - - -
25 x 25 Filter
(635 x 635 mm)
Factory-Accessory
Washable
Factory-Accessory
Media
*
Representative After-Market Filter Media
*
Fiberglass
*
Pleated
*
CFM L/s (1-in. / 2.5 cm) (4-in. / 10 cm) (1-in. / 2.5 cm) (2-in. / 5 cm) (1-in. / 2.5 cm) (2-in. / 5 cm)
800 (378) 0.03 (9) 0.03 (8) 0.05 (12) 0.07 (18) 0.17 (43) 0.11 (28)
1000 (472) 0.04 (11) 0.05 (12) 0.06 (16) 0.09 (24) 0.22 (55) 0.15 (37)
1200 (566) 0.05 (13) 0.07 (17) 0.08 (20) 0.12 (31) 0.27 (68) 0.18 (47)
1400 (661) 0.06 (15) 0.09 (23) 0.10 (24) 0.15 (38) - - 0.23 (58)
1600 (755) 0.06 (16) 0.12 (31) 0.11 (29) 0.18 (45) - - 0.28 (69)
1800 (850) 0.07 (18) 0.14 (35) 0.13 (34) 0.21 (53) - - - -
2000 (944) 0.08 (19) 0.16 (41) 0.16 (39) 0.24 (61) - - - -
2200 (1038) 0.08 (21) 0.19 (49) 0.18 (45) 0.28 (70) - - - -
*. Representative estimates from filter manufacturer data sheets. See manufacturers’ specifications for pressure drop versus airflow data for specific filter media.
Face Velocity
Factory-Accessory
Washable
Representative After-Market Filter Media
*
*. Representative estimates from filter manufacturer data sheets. See manufacturers’ specifications for pressure drop versus airflow data for specific filter media.
Fiberglass
Pleated
*
FPM  (m/s) (1-in. / 2.5 cm) (1-in. / 2.5 cm) (2-in. / 5 cm) (1-in. / 2.5 cm) (2-in. / 5 cm)
200 (1) 0.04 (10) 0.05 (13) 0.08 (20) 0.18 (47) 0.12 (31)
300 (1.5) 0.05 (14) 0.09 (22) 0.13 (34) 0.30 (75) 0.21 (52)
400 (2) 0.07 (17) 0.13 (32) 0.20 (50) - - 0.31 (78)
500 (2.5) 0.08 (21) 0.18 (44) 0.27 (69) - - - -
600 (3) 0.09 (23) 0.23 - - - - - - -
700 (3.6) 0.10 (26) 0.29 - - - - - - -
Table 7 – Filter Media Pressure Drop (Clean) Versus Airflow - in. w.c. (Pa) (Continued)
FURNACE 
CASING 
WIDTH
*
*. Not all families have these models
FILTER SIZE
FILTER 
TYPE
†
†. Recommended to maintain air filter face velocity. See Product Data for part 
number
SIDE RETURN
BOTTOM 
RETURN
14-3/16 (360) 
16 x 25 x 3/4
(406 x 635 x 19) 
14 x 25 x 3/4
(356 x 635 x 19) 
Washable 
17-1/2 (445)
16 x 25 x 3/4
(406 x 635 x 19) 
16 x 25 x 3/4
(406 x 635 x 19) 
Washable 
21 (533)
16 x 25 x 3/4 
(406 x 635 x 19) 
20 x 25 x 3/4
(508 x 635 x 19) 
Washable 
24-1/2 (622)
16 x 25 x 3/4
(406 x 635 x 19) 
24 x 25 x 3/4
(610 x 635 x 19) 
Washable 
FILTER 
CABINET 
HEIGHT - IN 
(MM)
FILTER SIZE - IN (MM)
*
*. Filters with a side return-air may have a different filter size. Measure the 
filter to obtain the correct size.
FILTER 
TYPE
†
†. Recommended to maintain air filter face velocity. See Product Data for part 
number.
16 (406)
(1) 16 x 25 x 3/4 (406 x 635 x 19) or
(1) 16 x 25 x 4-5/16 (406 x 635 x 110)
Washable or 
Media
20 (508)
(1) 20 x 25 x 3/4* (508 x 635 x 19) or
(1) 20 x 25 x 4-5/16 (508 x 635 x 110)
Washable or 
Media*
24 (610)
(1) 24 x 25 x 3/4* (610 x 635 x 19) or
(1) 24 x 25 x 4-5/16 (610 x 635 x 110)
Washable or 
Media*