Thermo Pride CHX3-75N Installation And Operation Manual page 34

All installations and services must be performed by qualified service personnel.
Figure 18A
All trunk lines, take-offs, registers and grill-free areas must be figured when determining the air handling
capacity of a duct system. One can obtain the necessary duct system size by utilizing the chart below.
(For example, see Figure 18A.) Use a supplier's catalog for proper sizing of outlet and return air registers
to insure that the register will meet the CFM requirements of the run to which it is connected.
The main trunk lines, take offs, registers and grills of the supply return air duct system must have an
adequate square inch area to move the desired CFM in order to achieve proper movement. The following
chart shows the CFM air handling capability based on a 0.1" SP loss in the supply duct system. The total
external static pressure should not exceed .2 inches water column.
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