Kees IFG (INDIRECT FIRED GAS) MAKE-UP AIR UNITS - Duct Furnace Installation & Maintenance Manual User Manual
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BYPASS SIZING INFORMATION
(BUILT ON THE JOB – NOT FURNISHED BY
FACTORY)
On occassion when a duct furnace is incorporated in
an air handling system, it may be desirable to handle a
total of more CFM than the duct furnace will pass at a
given static pressure drop and temperature rise. There-
fore, it is necessary to arrange to bypass the additional
CFM required. The size of the bypass duct can be
determined by referring to the chart. This permits the
static pressure drop through the bypass to balance off
the drop through the heat exchanger. The bypass duct
is not factory furnished and must be built on the job by
the installer and a damper placed therin if required.
USE OF BYPASS CURVES
The width of the by-pass for CFM in excess of that
provided through the heater may be found in the
following manner:
1. Determine the CFM and pressure drop through the
heater based on the heating requirement
specifications.
2. Determine the additional CFM desired, over and
above the CFM for the heating requirements.
3. Using the pressure drop which was determined from
performance curves above, for the heating load,
locate this pressure drop on the by-pass curves.
Follow this curve until it intersects thevertical CFM
line for the excess CFM desired.
4. Follow horizontal line to left to obtain width of by-pass
duct.
Figure 5 - By-Pass Curve