Catalogue

UH-PRC002-EN 17
Selection Procedure
High Efficiency Duct Furnace
1. From the performance data tables, select the unit whose heating output meets or exceeds the
heating load requirement.
2. Given the airflow to be supplied to the duct furnace, temperature rise and pressure drop
through the duct furnace can be read directly from the performance data charts. If the air
temperature rise is below 30°F, some supply air must be bypassed around the duct furnace. If
the air temperature rise is over 80°F, additional supply air must be delivered to the duct furnace.
Selection Example—A natural gas duct furnace that can provide 300 MBh heating output is
required. An airflow of 5,000 cfm is being provided to the duct furnace.
Select the unit as follows:
a. From Table 14, p. 27, select a GLND-040 with a 400.0 MBh input and 320.0 MBh heating
output.
b. From Figure 10, p. 29, temperature rise at 5,000 cfm is 58°F and pressure drop is 0.16 inches.
Horizontal Blower Assembly
1. From the performance data tables, select the blower assembly that provides the needed airflow
at the required static pressure, and determine the required motor size and fan speed.
2. If a blower assembly is to be used with a duct furnace, refer to the dimensional data table to
determine which blower to use with the given duct furnace. The duct furnace pressure drop
must be added to the pressure drop of the duct system before entering the blower assembly
performance data tables. Enter the performance data table at the required airflow and at the
total external static pressure to determine the motor size and fan speed.
Selection Example—A GLND-040 high efficiency duct furnace is to be used with a horizontal
blower assembly. An airflow of 5,000 cfm is required. The pressure drop of the duct system is
0.54 inches, and the pressure drop of the duct furnace is 0.16 inches.
Select the unit as follows:
a. From Table 29, p. 55, select a HBAC-45 for use with the GLND-040 duct furnace.
b. From Table 16, p. 28, an HBAC-45 at 5,000 cfm and 0.7 inches static pressure (0.54-inch
ductwork + 0.16-inch furnace) requires a 1-1/2 hp motor with a fan speed of 720 rpm.