Kees IFG (INDIRECT FIRED GAS) MAKE-UP AIR UNITS - Duct Furnace Installation & Maintenance Manual - Manual (Page 6)

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PERFORMANCE DATA CURVES
Figure 3 - High Temperature Rise Duct Furnaces — 30-90 F° (17-50 C°)
Figure 4 - Low Temperature Rise Duct Furnaces — 20-60 F° (11-33 C°)
Pressure drop through the heat exchanger is based on
the CFM throughput. The desired data is obtained in
the following manner:
1. Select heater size based on heat loss of the building
to be heated.
2. Select temperature rise desired.
3. Based on temperature rise, the horizontal line inter-
sects heater temperature vs. CFM curve.
4. Follow vertical line down to select CFM.
5. For pressure drop selection, follow vertical CFM line
until it intersects the selected heater performance
curve vs. pressure drop.
6. Follow the horizontal pressure drop line to the left,
and read pressure drop of the selected heater.