Placeholder Duct / Real Duct Conversion

Good evening everyone. I am trying to write a Dynamo script that is capable of converting Ductwork to placeholder ductwork, and vice versa.

I know that Revit can change placeholder to duct without Dynamo, but in my case, I would actually like to invert this process and change it back to placeholder.

I do not know if this is possible because they are in different categories. I tried grabbing the family type ID numbers of Duct (and Placeholder Duct) and attempted to reassign them to family instances, but it is not successful.

Could anybody shed some light on the topic? I would like to develop this further but I am not sure if this can be done, or if anyone has been down this road before.


The following way involves a bit of direct interaction with Revit API. But I’d recommend to take a look at some of the existing packages, there might be one that does this conversion already.

Duct class has a method named CreatePlaceholder requires system type, duct type, level, start point and end point. So the process will be like:

  • Collect required data from existing ducts first.

  • Create plaecholders.

  • Remove ducts.

The obvious disadvantage of this approach is losing annotations since it removes the ducts eventually. Tags attached to these ducts will be gone. But I suppose if you are using placeholders all the time then the design is not fixed yet, so losing annotation is not much of loss.

Thanks for the suggestion, Jshial. I haven’t dabbled in API yet, but perhaps I should.

In any case, I think I may have found an alternate route to solve my dilemma.

The whole idea was that we wanted some duct to be shown as single-line, and other duct to be shown as double line, all within the same view. I was trying to accomplish this by using placeholder.

However, I am now going to try having two separate views superimposed atop one another on a sheet. One will have the applicable double-line ductwork, while the other will be coarse detail and only have the applicable single-line ductwork.

I read a similar post from @Greg_McDowell reg_McDowell in Aug '16 concerning piping.

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