Technical Guide

505428-YTG-O-0413
70 Johnson Controls Unitary Products
Additional Static Resistance (Continued)
CFM Static Pressure and Power-Altitude and
Temperature Corrections
The information below should be used to assist in application
of product when being applied at altitudes at or exceeding
1000 feet above sea level.
The air flow rates listed in the standard blower performance
tables are based on standard air at sea level. As the altitude
or temperature increases, the density of air decreases. In
order to use the indoor blower tables for high altitude
applications, certain corrections are necessary.
A centrifugal fan is a "constant volume" device. This means
that, if the rpm remains constant, the CFM delivered is the
same regardless of the density of the air. However, since the
air at high altitude is less dense, less static pressure will be
generated and less power will be required than a similar
application at sea level. Air density correction factors are
shown in Altitude Factors Table and Temperature Correction
Figure.
Model CFM Hot Water Coil Steam Coil
NC300
8000 0.06 0.11
9000 0.07 0.14
10000 0.08 0.17
11000 0.09 0.20
12000 0.10 0.23