Simple Guide to Master AutoCAD MEP (Ducting)

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About: Hi! I am an Electrical Engineer. I live and work in Malaysia! Nice to Meet You!

AutoCAD MEP may seem to be not much different from AutoCAD, but when it comes to drawing Mechanical, Electrical & Plumbing (MEP) services, it can definitely help you save a lot of time and effort - provided you are well equipped with the basics. AutoCAD MEP does not differ much from AutoCAD, and in this session you will be able to learn how to draw a duct system using AutoCAD MEP.

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Step 1: Open Your Tool Palette Window

The AutoCAD MEP Tool Palette contains all the basic tools required to construct different systems - Pipes, Ducts, Schematics, etc. If your tool palette does not show, in the Command Bar, type in TOOLPALETTES and hit enter / space bar. The Tool Palettes should appear by the side.

Step 2: Setting the Tool Palette

To select the type of services that we want to draw, right-click on the Tool Palettes top bar (highlighted in red), and then select the service that we want to draw. In this case, since we are going to construct a ducting system, we select HVAC (Heating, Ventilation, & Air-Conditioning System).

Step 3: Start Drawing Your Duct

Click on “Duct” or the desired duct system (Outdoor/Fresh Air, Supply Air, Return Air, Exhaust Air Duct), or the desired shape of Duct to start routing. AutoCAD MEP has its own preset systematic layering convention that automatically orders each ducting system into separate layers. For example, when we draw an exhaust duct, it is automatically put into the layer named “M-Duct-Exhs”, whereas for Supply Air Duct, it is put under the layer “M-Duct-Sply-Medm”. Different Ducting System is also colored differently, and those color codes can be modified by changing the colors for the layer.

In case you are new to AutoCAD, layering is an important feature in AutoCAD that enables designers to systematically “turn off” and “turn on” different systems wherever required.

Step 4: Set Properties to the Duct – Before the Duct Segment Is Finished Constructed

We can set properties for the duct (Sizes, Types,, Elevation, Fittings) after a duct is constructed, or more easily, during the preview mode before the duct is formed. Preview will be shown for every segment of duct right before you click on where you want that segment to stops. The previewed duct can be adjusted by hovering your cursor around to extend the length, and to the properties palettes to edit the properties of the duct segment to form. Preview is constructed with the click.

So the simple step is as follow:

Click on where you want to begin the duct. In this case, we are going to route a supply air duct starting from the AHU (Air Handling Unit) in the AHU room. After clicking on your first point, before we move on to the next point to complete the first section of our duct, we specify the properties for this first section of duct at the properties palette. Therefore, after our first click and before our second click, hover our cursor to the properties pane to set the properties for this first section of duct. In this case, we set the rectangular duct at 500(W)x500(H), at an elevation of 3000 (from Floor). The elevation can be neglected (all set to 0) if we are just going to draw in 2D, but even in that we can utilize positive or negative elevation values to indicate duct rising or dropping.

Note: If your properties pane does not show, type in the command bar “PROPERTIES”.

Step 5: Or, Set Properties of the Duct Segment – After Duct Is Constructed

After we set all the properties for this section of duct, for example, its size, its system type, its shape, and etc. hover our cursor toward where we want this section of duct to end and click on it. Before we click on, we can observe that the preview that is shown will reflect the properties that we set for the section desired. For example, the preview shows a broader duct if the duct width is set higher (Height of duct is the thickness which can only be reflected in duct size label or in elevation). After the click, the preview turns into “real” constructed section of duct, where the properties of the section is still editable in the properties pane.

Step 6: Make a Bend – With Specific Angle

To make a bend, keep the route going as you would want your duct to head after your previous click. AutoCAD MEP sets the degree at specific angles to help us draw faster. If we would like the duct to bend at other specified angles, we can set it (while in the preview mode, i.e. while drawing the duct) in the property pane, under Routing > Bend Angle. Similarly, we can set other properties for this second section of duct that we would like to construct by setting them in the properties pane, again, before we click on where we want this section of duct to end.

Step 7: Make a Bend – Selecting a Fitting for It

By clicking on the second point, the second section of duct is constructed. Because this time it involves a bend, AutoCAD will prompt a message to ask which type of bend you would like to include in your routing. Select the type of elbow that you want. In this case, we will be selecting the common Rectangular Smooth Radius 1W Elbow, and then click ‘OK’.

Step 8: Start Your Duct Routing!

Keeps routing the duct for the second, third and subsequent segments of the duct, while setting the properties (sizes or etc. of each of the segments) before clicking on the end of each segment of duct.

Step 9: Make a Transition (Reducer)

Again, when we would like to reduce the size of duct after a segment is constructed, a message will pop up to ask which type of reducer we would like to use for our transition. Select a suitable reducer from the given list and click ‘OK’.

Step 10: Extend a Duct After Constructed

We can construct the duct throughout and continuously without the need to press ‘ESC’ when we change duct properties from one segment to another. If it happens that you need to do so, to resume your duct routing, select the last duct segment and click on the small ‘+’ sign at the end of the duct and continue routing.

Step 11: Keep Going, Until the Last Segment.

Keep on routing until you reach the end of duct. Hit Enter to finish.

On an extra note, AutoCAD MEP might experience some software issue where the double lines duct turns into single lines at certain portions (and the duct sizes or labels disappears). The symptoms go on and off with some instances where some parts of ducts return to normal while some do not. Sometimes it is weirdly acting like a "contagious disease" that spreads to adjoining ducts when the duct is extended to join.

This has something to do with the issue to refresh/regenerate the graphic. If you happen to experience this, the solution is simple. Save your work, close the application and restart it. Everything should turn back to normal since then.

Step 12: Add a Duct Fitting

When you reach the end of the duct run, to add an end cap to the end of the segment, or in other words, to add a duct fitting, click the ‘fitting’ tab in the tool palette, and select end cap.

Step 13: Add a Duct Fitting

Then, in the properties pane, a simple picture of the part that we are going to add will show in the display tab. If the fitting to add is not what we desire, for example, the fitting shown is not an end cap, click on the picture of the part to initiate the “Select Part” window. From the select part window, we can select various types of fittings that we want to customize to the types of fittings in our tool palette. Some of the examples of fitting types include Wye, Elbow, Vee, Tee, Takeoffs, Cross or etc.

Step 14: Add a Duct Fitting / Extend Existing Ducts

After selecting the right fitting, which in this case, End Cap, click ‘OK’. Then, hover your cursor to the end of duct or wherever you want to place your fitting at, and click on it when a green snap icon appears. Then, click for a second time on where you want to orient the fitting to, or simply hit ENTER/space bar. The fitting shall automatically fit the duct size, or we would adjust it manually from the properties pane.

Step 15: Add a Duct Fitting - by Presetting a Routing Preference

Previously, we learnt to set the fittings spontaneously when a window pops up to ask us what fitting we want to use at each bends or transitions. The preference of selection of these fittings is called the ‘Routing Preference’, and can be set through the following manner. To know what style of routing preference we are using, start drawing your duct. Like any other properties of duct, it will only appear when you are under the command of drawing your duct, and will disappear when you ESC from your “preview mode”.

Step 16: Set Routing Preference

Stick to Generic Slip Joint as the style of your routing preference, and set your preferences for ‘Generic Slip Joint’ through the following steps. Go to the ‘Manage’ tab, under ‘Style Manager’, HVAC Routing Preference

Step 17: Set Routing Preference

Under your current drawing file name > HVAC Objects > Duct Part Routing Preferences > Generic Slip Joint (Double-click)

Step 18: Set Routing Preference

Now, we can set the routing preference for the style ‘Generic Slip joint’ that we are using for our routing. In this case, we would like to custom our rectangular duct routing to present a Smooth Radius 1W elbow for 90 degree straight bend, Beveled tap as takeoffs, and concentric duct transition as reducers. This way, whenever this Routing Preference Style (Generic Slip Joint) is selected, the above fittings will automatically be in place when we come across Bends, Tees, and Transitions, respectively. After setting for all fittings we desire, click ‘OK’ and save.

Step 19: Adding a Branch Fitting – Tees or Takeoffs

Now, let us try drawing a branch from our main duct with a beveled tap. In the ‘preview mode’ again (or halfway when you are drawing your duct), all duct properties should appear at the properties pane. Under Advanced > Routing Options > Branch Fitting, set whether you want your branch fitting to be Tee or Takeoff. Because we want to add a beveled tap, i.e. a takeoff, we set this option to ‘Takeoffs’. If we set to ‘Tee’, the ‘Tee’ fitting that we set for step 18 (if any) will be in place.

Step 20: Adding a Beveled Tap – Take Off

Because we have set beveled tap as the preferred takeoff fitting, when select takeoff as the branch fitting at the properties pane, when we extend the branch duct to snap to the main branch, the beveled tap fitting will appear automatically.

Always Hit Enter to finish adding any kind of fittings.

Step 21: Setting the Snap Settings – for Fittings to Add Automatically

If you have trouble snapping to the main duct, go to snap setting and check important snap preferences such as nearest or perpendicular. The duct fitting will be added automatically, provided you manage to snap your branch duct to your main duct exactly at the edge or center. As mentioned, hit ‘ENTER’ or space bar to complete the routing.

Note: Snap settings are sometimes tuned off. Turn it on/toggle it by hitting 'F3'. Snapping can also be affected by elevation of adjoining ducts. Remember to set them to the same level, otherwise a duct riser will be automatically included to enable connection.

Difference of leveling can also be reflected in the view of the drawing, where ducts with higher elevation appears on top and the lower ones appears behind and with faded, dotted lines.

Step 22: Toggle Takeoff's Direction

To change the direction of the bevel, select the beveled tap and click on the small arrow head. The direction of the bevel can be toggled repeatedly.

Step 23: Duct Parameter/Duct Size Annotation/Label

All duct sizes should automatically appear. To add annotation or duct size manually (sometimes we have to delete duct size labels when it blocks our snap from main duct to branch ducts), simply select the duct segment we want to label, go to the ‘Annotate’ tab, under ‘Label’ > MEP Label, hover to where we want to place the label at and then click on it. To add multiple labels faster, do it the other way round. Go to annotate tab > MEP Label, then only select the duct segment and hit 'Enter'. When the label's preview appears, click on where we want the label to be at.

To select the style of label (or the parameter that we want to label), set the style in the properties pane while selecting the label or before placing the label. ‘Standard – Duct’ will be a label for the duct Width x Height, while other parameters such as elevation or Flow rate are also available in the list.

Step 24: Replacing a Fitting

To replace fittings, there is no need to delete and reconstruct the involved duct segments. All we need to do is to select the fittings (multiple can be selected using the "SELECTSIMILAR" command) and all selected can be replaced all at once. Similar fittings are encouraged to be selected for this function because there might be compatibility issues replacing fittings from different systems or types. After clicking on ‘Replace Fitting’, type in E for Elbow, or T for Tee in the command bar, and hit enter. The ‘Choose a Part’ window will pop up again, and by selecting the desired fitting and hit ‘OK’, all selected fittings will be replaced, where possible, to this new fitting selected.

Step 25: ‘Split’ or Break Ducts Into Segments

If you have finished constructing your duct only to realise you need to make transitions in between a segment, there is a way where you do not need to delete and redraw the segment. The method is to split the duct segment into 2 or multiple segments and then change the size for each of the segment as desired. This is almost the same as the ‘SPLIT’ command in Autodesk Revit, but here in AutoCAD MEP, the command is ‘BREAK’. Simply type ‘BREAK’ in the command bar and hit enter, click on the first point, followed by the second point of the splitting gap you want to separate the involved duct segment. This gap will separate our duct segment into 2, each of which can be adjusted to individual sizes or properties. After setting, join them back together.

"BREAK" is a command that you are finding if you want to change the size of duct at a certain points on a duct of the same size (to add a reducer) that is already constructed so you do not need to redraw the entire segment.

Step 26: Adding a Dovetail Wye.

One of the challenges that many people face is to add a rectangular dovetail Wye to our ducting system. A Wye fitting is very common in HVAC ducting systems, but adding this type of Wye seem to be a problem for most designers in CAD MEP. However, it is not as complicated as you think it will be, but can be done, in fact, within minutes of time.

Go to Tool Palettes > Fitting tab > Click Vee
In the properties pane > Design tab > Basic > Click on the Part (Diagram of fitting in the properties pane) > Select Part from Catalog > Wye > Asymmetric Dovetail Wye US Metric. The Asymmetric Dovetail Wye allows 3 different inputs of duct opening, whereas Symmetrical ones can only have equal sized openings to duct connectors.

Step 27: Add Selected – to Add Fittings

If you find looking for fittings in the catalog troublesome, and prefer to copy fittings from other drawing, the ‘Add selected’ function is good for you. Select a fitting that is readily available in the drawing, right-click, and click ‘add selected”. Go to where you want to add the fitting to, click on a point in the duct and orient it to where it is supposed to, and then click for a second time to add the fitting in.

Bear in mind that AutoCAD MEP has elevations (difference in heights). Fittings or duct segments from different height levels may not be able to join properly. We can either set both adjoining parts to be of the same elevation, or accept a drop/rise to be appearing in between the 2 heights of ducts.

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