Change MEP system type


Is it possible to change the MEP System Type, if an object has “undefined” in the System type parameter?

I will just put this at the front again.

No one has a possible solution for this?

I think I made a mistake, when I took the Air terminal element. I should be the connector I want to find.

I’m not very familiar with MEP. However, letting us know what error is being thrown up might help.

This is the failure I get









As I write in my second post, I thought I had to use connector element instead of AirTerminal element, but this gave me an empty list

Hi Simon,

The error that you are getting with the “Element.SetParameterByName” node is because the value “System Type” should be set up as mechanical system. This can be seen in my dynamo script.


So far what I’ve experienced is for example if some duct has its “System Type: Undefined” it can’t be changed. Furthermore if you manually try to change it within revit, you will see that you can’t do it as well. I think this issue is related to some constraint in the revit API, but maybe with a costume python script this approach can be done. On the other hand for example if ducts have the system type defined this approach will work.

Best regards,

Alejandro Mata

Hello Alejandro

Thank you for your reply.

I will try to see, if I cant do something like you show.

I dont know if it is an issue, but I dont want it on ducts, but on Air Terminals, where I do not have any ducts connected.

It is because the script is just one little part of a total workflow I working on

A part of the workflow I place air terminals in the model, and when they are placed, their System Type is undefined.



Hi Simon,

You’re welcome.

Regarding the “System Type” of the air terminal devices is an “only read” instance parameter. This means that you “can’t” really modify it. Maybe by using a python costume node via revit API could be done. Basically almost everything is possible with dynamo + python :slight_smile:

However, I’m not sure if you will get some benefit setting up the “System Type” parameter of air terminal devices without connecting them to any ducts. This instance parameter in air terminal devices will be always determined by the “System Type” of the ducts which are connected to. That’s why, I showed you before this approach applied in ducts.

Kind regards,

Alejandro Mata

You right, that I can get the system type from the duct I will connect, and of course I will connect the ducts and Air Terminals at some point in a project.

But if I could give the Air Terminal the correct system type before the ducts is connected, then it will be one less reason to connect Air Terminals to wrong systems.

I have a excel file where I define which AHU supply which rooms, and with this information I am able to give the right System Type to all Air Terminals.