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Loop in Ductwork Error

When I try to calculate the CFM for my ductwork, I get the following error:​

warning

There is a loop in your ductwork.
Calculations will be incorrect until the loop is removed.
Calculations in ducts that are not in the loop are correct.
If you do not see any loops, try running "Coordinate Drawing and Database".
The duct with the loop in it is on drawing <Drawing Name>.

Cause​

As the error message indicates, there is a closed loop somewhere in your system. If there is a loop in your ductwork, Design Master HVAC cannot calculate the CFM.

Solution​

First, you need to find where the closed loop is located in your system.

If you cannot find the loop on the indicated drawing, run the Coordinate Drawings and Database command on that drawing. It is possible that a duct that is in the database but not currently on the drawings is causing the problem. Running this command will force the duct onto the drawing.

Once you find the loop, you must remove it. If your design requires a loop, you need to model it in DM HVAC such that the loop does not close by following these steps:

  1. Choose a middle point in the loop, then draw the ductwork from two sides that meet at that point.

  2. Run the No Fitting command.

  3. Select the point where the two ducts meet. This will remove the end cap fitting from each of the ducts and they will appear to be a continuous section.

A correctly modeled loop is shown below.