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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 below.
NOTE: The filter pressure drop values in the "Filter Perfor-
mance" table shown below are typical values for the type of
filter listed and should only be used as a guideline. Actual
pressure drop ratings for each filter type vary between filter
manufacturer.
RECOMMENDED FILTER SIZES
Input/Output
Cabinet
CFM
BTU/H
Size
40/38
1200
A
60/56
1200
B
80/75
1200
B
80/75
1600
C
100/93
1600
C
100/93
2000
C
120/112
2000
D
APPLYING FILTER PRESSURE DROP TO
DETERMINE SYSTEM AIRFLOW
To determine the approximate airflow of the unit with a filter in
place, follow the steps below:
1.
Select the filter type.
2.
Select the number of return air openings or calculate the
return opening size in square inches to determine the
proper filter pressure drop.
FILTER PERFORMANCE - PRESSURE DROP INCHES W.C.
Minimum Opening Size
Airflow Range
1 Opening
Sq. in.
0 - 750
230
751 - 1000
330
1001 - 1250
330
1251 - 1500
330
1501 - 1750
380
1751 - 2000
380
2001 & Above
463
UNIT CLEARANCES TO COMBUSTIBLES
Top
Application
In.
Upflow
1
Unitary Products Group
Side Return
Bottom Return
Filter in.
Filter in.
16 x 25
14 x 25
16 x 25
16 x 25
16 x 25
16 x 25
16 x 25
20 x 25
16 x 25
20 x 25
16 x 25
20 x 25
(2) 16 x 25
22 x 25
Disposable
2 Openings
1 Opening
Sq. in.
In w.c.
0.01
0.04
0.08
0.08
658
0.14
658
0.17
658
0.17
Front
Rear
Left Side
In.
In.
In.
3
0
0
3.
Determine the External System Static Pressure (ESP)
without the filter.
4.
Select a filter pressure drop from the table based upon
the number of return air openings or return air opening
size and add to the ESP from Step 3 to determine the
total system static.
5.
If total system static matches a ESP value in the airflow
table (i.e. 0.20, 0.60, etc,) the system airflow corre-
sponds to the intersection of the ESP column and Model/
Blower Speed row.
6.
If the total system static falls between ESP values in the
table (i.e. 0.58, 0.75, etc.), the static pressure may be
rounded to the nearest value in the table determining the
airflow using Step 5 or calculate the airflow by using the
following example.
Example: For a 120,000 Btuh furnace with 2 return openings
and operating on high speed blower, it is found that total sys-
tem static is 0.58" w.c. To determine the system airflow, com-
plete the following steps:
1.
Obtain the airflow values at 0.50" & 0.60" ESP.
Airflow @ 0.50": 2285 CFM
Airflow @ 0.60": 2175 CFM
2.
Subtract the airflow @ 0.50" from the airflow @ 0.60" to
obtain airflow difference.
2175 - 2285 = -110 CFM
3.
Subtract the total system static from 0.50" and divide this
difference by the difference in ESP values in the table,
0.60" - 0.50", to obtain a percentage.
(0.58 - 0.50) / (0.60 - 0.50) = 0.8
4.
Multiply percentage by airflow difference to obtain airflow
reduction.
(0.8) x (-110) = -88
5.
Subtract airflow reduction value to airflow @ 0.50" to
obtain actual airflow @ 0.58" ESP.
2288 - 88 = 2197
Filter Type
Washable Fibers
2 Opening
1 Opening
In w.c.
In w.c.
0.01
0.03
0.07
0.07
0.08
0.13
0.09
0.15
0.09
0.15
Right Side
Flue
In.
In.
0
0
246738-YTG-B-0806
Pleated
2 Opening
1 Opening
In w.c.
In w.c.
0.15
0.20
0.20
0.25
0.06
0.30
0.07
0.30
0.07
0.30
Floor/
Closet
Bottom
Alcove
Combustible
Yes
2 Opening
In w.c.
0.17
0.17
0.17
Attic
Yes
5
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