Filter
Top Products
Unitary Products Group 5
036-21560-002 Rev. A (1204)
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. Determine the External System Static Pressure (ESP)
without the filter.
3. 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.
4. 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.
5. 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 130,000 Btuh furnace operating on high
speed blower, it is found that total system static is 0.58" w.c.
To determine the system airflow, complete the following
steps:
1. Obtain the airflow values at 0.50" & 0.60" ESP.
Airflow @ 0.50": 2125 CFM
Airflow @ 0.60": 2035 CFM
2. Subtract the airflow @ 0.50" from the airflow @ 0.60" to
obtain airflow difference.
2035 - 2125 = -90 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 (-90) = -72
5. Subract airflow reduction value to airflow @ 0.50" to
obtain actual airflow @ 0.58" ESP.
2125 - 72 = 2053
FILTER PERFORMANCE - PRESSURE DROP INCHES W.C. AND (KPA)
AIRFLOW RANGE
MINIMUM
OPENING SIZE
FILTER TYPE
DISPOSABLE
WASHABLE FIBER
*
PLEATED
CFM
in
2
In W.C. In W.C. In W.C..
0 - 750 230 0.01 0.01 0.15
751 - 1000 330 0.05 0.05 0.20
1001 - 1250 330 0.10 0.10 0.20
1251 - 1500 330 0.10 0.10 0.25
1501 - 1750 380 0.15 0.14 0.30
1751 - 2000 380 0.19 0.18 0.30
2001 & Above 463 0.19 0.18 0.30
*. Washable fibers are the type supplied with furnace (if supplied).
UNIT CLEARANCES TO COMBUSTIBLES
APPLICATION TOP FRONT REAR
LEFT
SIDE
RIGHT
SIDE
FLUE
FLOOR/
BOTTOM
CLOSET ALCOVE ATTIC
LINE
CONTACT
DOWNFLOW130000
1"
*
YES YES YES NO
HORIZONTAL030110COMBUSTIBLENOYESYES
YES
†
*. Special floor base or air conditioning coil required for use on combustible floor.
†. Line contact only permitted between lines formed by the intersection of the rear panel and side panel (top in horizontal position) of
the furnace jacket and building joists, studs or framing.