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How to Make Dashed Ductwork

Posted on January 22nd, 2010. Last updated on June 15th, 2023.

It is possible to make ductwork that is dashed using Design Master HVAC, but there are some limitations.

Set the Layer System Options Correctly

Run the Layers command.

Select the layer system that you want to be dashed on the Layer System grid. Press the Edit System button.

Uncheck the Ducts are solid box.

Press the OK button to save your changes and return to the Layers dialog box.

Set the Main Ductworks to Not Plot

The layers used for the main ductwork need to be set to not plot. With the same Layer System active, select the following layer keys in the Layer Key grid in the top right.


For each layer key, uncheck the Plot box in the grid at the bottom of the dialog box.

Set the Linetype of the Hidden Ductwork Layers

The layers used for the hidden ductwork need to be set to the dashed linetype you want to use. With the same Layer System active, select the following layer keys in the Layer Key grid in the top right.


For each layer key, set the Linetype column in the grid at the bottom of the dialog box to DM_DM-DASHED.


The first limitation is that the lines will appear continuous while you are working on the drawing in both model space and paper space. It is important for the double-line redraw function that you do not freeze the non-plotting duct layers.

The second limitation is that dashed duct systems will no longer generate hidden lines automatically. You will need to draw those in yourself.

The limitations are an unfortunate result of how AutoCAD generates hidden lines and not something that we can work around.

Updating Existing Drawings

If you make these changes in a project where you already have demo ductwork drawn, run the Update Drawing Layers to Match Project List command to update the layers in your drawing to match the changes you made in the Layers dialog box.

Redraw the double-line on the demo ductwork using the Draw Double Line (Branch) or Draw Double Line (Window) command.

How it Works

Normally, the main ductwork lines are drawn at the proper elevation for the ductwork using faces. Hidden ductwork lines are drawn at a very high elevation.

When the AutoCAD HIDE command is run, the faces properly obscure other faces below them. The dashed hidden lines always appear.

Unfortunately, the face entities used for the main ductwork always appear as a CONTINUOUS linetype, no matter what setting you choose for it.

When you uncheck the Ducts are solid box, the hidden lines are drawn at the same elevation as the faces.

Setting the faces to not plot turns them off so they do not appear on your final drawing and all you see are the dashed hidden lines. The hidden lines can display your dashed linetype.

Even though the faces do not plot, they still hide items, giving you some of the benefits of automatically hidden lines.

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