036-21610-002 Rev. A (1104)
Unitary Products Group
5
* Washable Fiber are the type supplied with furnace (if supplied).
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.
Calculate the return opening size in square inches to
determine the proper filter pressure drop.
3.
Determine the External System Static Pressure (ESP)
without the filter.
4.
Select a filter pressure drop from the table based upon
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 130,000 Btuh furnace with 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": 2110 CFM
Airflow @ 0.60": 2020 CFM
2.
Subtract the airflow @ 0.60" from the airflow @ 0.5" to
obtain airflow difference.
2020 - 2110 = -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.
2110 - 72 = 2038
FILTER PERFORMANCE - PRESSURE DROP INCHES W.C.
Airflow Range
Minimum
Opening Size
Filter Type
Disposable
WASHABLE
FIBER*
Pleated
1 Opening
1 Opening
1 Opening
1 Opening
CFM
In³
inwc
inwc
inwc
0 - 750
230
0.01
0.01
0.15
751 - 1000
330
0.05
0.05
0.2
1001 - 1250
330
0.1
0.1
0.2
1251 - 1500
330
0.1
0.1
0.25
1501 - 1750
380
0.15
0.14
0.3
1751 - 2000
380
0.19
0.18
0.3
2001 & Above
463
0.19
0.18
0.3
UNIT CLEARANCES TO COMBUSTIBLES
APPLICATION
TOP
FRONT
REAR
LEFT SIDE RIGHT SIDE
FLUE
FLOOR/
BOTTOM
CLOSET ALCOVE ATTIC
LINE
CONTACT
In.
In.
In. In.
In. In.
DOWNFLOW
1 6 0
0
3
6 1
1
YES
YES
YES
NO
DOWNFLOW B-VENT
1
3
0
0
0
1
1
1
YES
YES
YES
NO
1
Special floor base or air conditioning coil required for use on combustible floor.
