14
MUA-SVX004B-EN
Bypass Sizing Information
Built On the Job (Not Furnished by Factory)
On occasion 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. Therefore, 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 therein 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 the vertical CFM line for the excess CFM desired.
4. Follow horizontal line to left to obtain width of bypass duct.
Figure 5. Bypass Curve
