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107272-UIM-B-1105
Unitary Products Group 25
APPLYING FILTER PRESSURE DROP TO
DETERMINE SYSTEM AIRFLOW
Example: For a 84,000 BTUH (38.06 kW) furnace with 1 return open-
ings and operating on high-speed blower, it is found that total system
static is 0.30” w.c. (0.075 kPa). To determine the system airflow, com-
plete the following steps:
Obtain the airflow values at 0.10 w.c. (125 Pa) & 0.20 w.c. (150 Pa)
ESP.
Airflow @ 0.10”: 1175 CFM (60.17 m
3
/min)
Airflow @ 0.20”: 1110 CFM (57.62 m
3
/min)
Subtract the airflow @ 0.10 w.c. (125 Pa) from the airflow @ 0.20 w.c.
(150 Pa) to obtain airflow difference.
1175 - 1110 = -65 CFM (2.55 m
3
/min)
Subtract the total system static from 0.10 w.c. (125 Pa) and divide this
difference by the difference in ESP values in the table, 0.20 w.c.
(150 Pa) - 0.10 w.c. (125 Pa), to obtain a percentage.
(0.30 - 0.10) / (0.20 - 0.10) = 0.5
Multiply percentage by airflow difference to obtain airflow reduction.
(0.5) X (-65) = -32.5
Subtract airflow reduction value to airflow @ 0.10 w.c. (125 Pa) to
obtain actual airflow @ 0.30 wc (144 Pa) ESP.
1050 - 32.5 = 1017.5
FINAL PROCEDURE
Install Furnace Doors
Install the lower door first by sliding the bottom of the door down until
the tabs on the casing base engage the slots in the bottom door end
cap. Then push the top of the lower door in until the door clips snap into
place. Install the upper door in a similar manner, first engaging the slots
in the top of the upper door on the tabs on the casing top. Then snap
the bottom of the upper door into place against the casing.
Finish and Trim
Alcove and Closet Installations may now be finished and trimmed as
necessary.
TABLE 14:
Blower Performance CFM
BLOWER PERFORMANCE CFM - DFAA066
FACTORY EQUIPPED WITH STANDARD BLOWERS AND FILTERS
EXTERNAL STATIC PRESSURE, INCHES WC (kPa)
Blower Speed
BTU/H (kW)
Input / Output
CFM
(m
3
/ min)
0.1 (0.025) 0.2 (0.050) 0.3 (0.075) 0.4 (0.099) 0.5 (0.124)
cfm cm/m cfm cm/m cfm cm/m cfm cm/m cfm cm/m
Single Speed - No Coil 66(19.34) / 53(15.55) 1050(29.73) 1175 33.3 1110 31.4 1050 29.7 1000 28.3 950 26.9
Single Speed - With Dry Coil 66(19.34) / 53(15.55) 1050(29.73) 1125 31.9 1070 30.3 1020 28.9 960 27.2 910 25.8
BLOWER PERFORMANCE CFM - DFAA084
EXTERNAL STATIC PRESSURE, INCHES WC (kPa)
Blower Speed
BTU/H (kW)
Input / Output
CFM
(m
3
/ min)
0.1 (0.025) 0.2 (0.050) 0.3 (0.075) 0.4 (0.099) 0.5 (0.124)
cfm cm/m cfm cm/m cfm cm/m cfm cm/m cfm cm/m
Single Speed - No Coil 84(24.62) / 67(19.63) 1250(35.39) 1370 38.8 1305 37.0 1245 35.3 1175 33.3 1100 31.1
Single Speed - With Dry Coil 84(24.62) / 67(19.63) 1250(35.39) 1265 35.8 1195 33.8 1120 31.7 1045 29.6 1015 28.7
BLOWER PERFORMANCE CFM - DFAH066
EXTERNAL STATIC PRESSURE, INCHES WC (kPa)
Blower Speed
BTU/H (kW)
Input / Output
CFM
(m
3
/ min)
0.1 (0.025) 0.2 (0.050) 0.3 (0.075) 0.4 (0.099) 0.5 (0.124)
cfm cm/m cfm cm/m cfm cm/m cfm cm/m cfm cm/m
Single Speed - No Coil 66(19.34) / 53(15.55 1050(29.73) 1155 32.7 1111 31.5 1055 29.9 995 28.2 920 26.1
BLOWER PERFORMANCE CFM - DFAH084
EXTERNAL STATIC PRESSURE, INCHES WC (kPa)
Blower Speed
BTU/H (kW)
Input / Output
CFM
(m
3
/ min)
0.1 (0.025) 0.2 (0.050) 0.3 (0.075) 0.4 (0.099) 0.5 (0.124)
cfm cm/m cfm cm/m cfm cm/m cfm cm/m cfm cm/m
Single Speed - No Coil 84(24.62) / 67(19.63) 1250(35.39) 1127 31.9 1062 30.1 1005 28.5 952 27.0 887 25.1
NOTES:
1. Airflow expressed in standard cubic feet per minute (cfm) and in cubic meters per minute (cm/m)
2. Return air is through louvered filter door only.
3. Motor voltage at 115V