Using Claude to Create a Supply Duct System

You can use AI prompts in Claude to place air handlers, ducts, and air terminals.

This example describes the layout using text prompts. Another example will illustrate how to use a sketch of the desired layout to place the ducts.

Place a new rectangular duct at level L2 down the center of the building

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Results

No tool for creating elements has appeared on the Revit connection, so I'll write a Dynamo script that places the duct.

I couldn't place the duct myself. The Revit connection on your computer still only shows which Revit sessions are running and has no tool for creating elements. place_center_duct_L2.py does the placement instead. Paste it into a Python Script node in Dynamo with Project1 open and run it.

It finds the building's outer limits from the walls and runs one duct along the long direction, through the middle. Each end stops 2 ft short of the outer walls. Since you didn't give a size or height, I picked these defaults. You can change them in the settings block at the top:

Size: 24" × 12"
Height: 10 ft above L2
Duct type: the first rectangular duct type in the model
System: Supply Air, if it exists

The script changes the model, so try it on a copy first. If it can't find a level called L2, it lists the levels the model has. It also stops with a message if the model has no rectangular duct type loaded, which can happen in a project not started from an MEP template.

Note: Be sure to specify a rectangular duct type that includes connection elements (with elbows, taps, or tees). The Default rectangular duct type doesn’t include these connections, so the centerline of each duct wil be placed accurately, but the ducts join. If that happens, select the ducts and change their type.

Add 4 branch ducts on each side of the existing central duct with air terminals at 8' above level L1

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Results

Still no element-creation tools on the Revit connection, so this is another Dynamo script that builds on the duct from the last one.

add_branches_and_terminals.py adds the branches. Run it the same way, in a Python Script node in Dynamo, after the central duct is in place. I couldn't place them myself, because the Revit connection still has no tool for creating elements.

The script finds the central duct by taking the longest rectangular duct on L2. It then adds 4 branches on each side, spread evenly along the main. Each branch has:

a tap off the main,
a horizontal run out to halfway between the main and the outer wall,
an elbow,
a vertical drop to an air terminal 8 ft above L1.

The branches use 8" round duct, or 10"×8" if the model has no round duct type. Size, spacing, branch count and terminal type are all in the settings block at the top.

Check the drop height before running it. The central duct sits 10 ft above L2, but the terminals are on L1. So every drop runs down through the L2 floor, a full floor height plus 2 ft. If the main is meant to serve the L1 ceiling, move it down to L1 first. In the central duct script, set LEVEL_NAME = 'L1' and choose an offset above 8 ft. The output reports the drop length so you can confirm it.

Two things can stop the script partway:

No air terminal family loaded. It stops with a message, so load a supply diffuser first. It needs a non-hosted family, because a ceiling-hosted diffuser won't place without a ceiling.
Missing fittings. Taps and elbows rely on your duct routing preferences. If a fitting can't be made, the duct is still placed, and the output lists which joints need connecting by hand.

As before, the script changes the model, so try it on a copy first.

Note: Be sure to specify a round duct type that includes connection elements (with elbows, taps, or tees). The Default round duct type doesn’t include these connections, so the centerline of each duct wil be placed accurately, but the ducts join. If that happens, select the ducts and change their type.

Dynamo returns this error

ERROR: 'ElementId' object has no attribute 'IntegerValue'

Traceback (most recent call last):

File "<string>", line 138, in <module>

AttributeError: 'ElementId' object has no attribute 'IntegerValue'

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Results

That line only builds the output summary. Revit 2024 renamed ElementId.IntegerValue to .Value, and later releases removed the old name. I'll fix it in all three scripts so they work on any version.

All three scripts are fixed and attached; paste the updated add_branches_and_terminals.py into your Python Script node and run it again.

The error came from your Revit version, not the duct logic. Revit 2024 and later number element IDs with .Value instead of .IntegerValue. The scripts now check which one your version has and use it, so they work on older and newer releases.

Check the model before you rerun. The error was on the line that records the first branch, which runs after that branch's air terminal, drop and horizontal duct were already placed. Dynamo may have kept those three elements when the script stopped. Look near the first spot along the main on one side. If you see a lone terminal with a duct, press Ctrl+Z or delete them first, so the rerun doesn't place a duplicate.

The central duct script had the same issue in its output line. If it showed an error earlier, the duct was still created, so check for it before running that script again.

Place an Air Handler component at 10' above level L2 and connect the rectangular duct to the supply connector

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Results

Next I'll write the AHU script, building on the same central duct.

place_ahu_connect_main.py places the air handler and connects it. Run it the same way in Dynamo; it already includes the Revit 2024+ fix.

It places the first Air Handling Unit type loaded in your model, 10 ft above L2, just past the start end of the central duct. It turns the unit so its supply outlet faces the duct, then lines the outlet up with the duct 6 ft from its end. It then runs new duct, the same size as the central duct, from the supply outlet into the duct's open end, with elbows where the heights differ.

Some things to check:

An AHU family has to be loaded. If none is, the script stops and says so. The Revit library has them under Mechanical > MEP > Air-Side Components > Air Handling Units.
Expect a short drop. The unit's base sits at 10 ft, the same height as the duct's centerline, so its outlet is higher than the duct. The connection goes out, down, then into the duct, and the output gives the height difference. If you'd rather have a straight run, lower AHU_OFFSET.
The outlet size may differ from the duct. If it does, the script adds a transition fitting. If your routing preferences have no transition, the output says the outlet wasn't connected, and you can join it by hand.
Which end it uses. It connects to the start end of the central duct. If the unit lands on the wrong end of the building, set MAIN_END = 'end'.

As before, the script changes the model, so try it on a copy first.

List the ducts

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Results

The model has 21 ducts, about 289 ft in total. All of them are on one system, Mechanical Supply Air 3 (Supply Air), and they use two duct types.

Rectangular main ("Mitered Elbows / Taps")

Id	Level	Size	Length	Flow	Velocity
1245546	L2	24"x12"	91'-0"	2,278 CFM	1,139 FPM
1245845	L2	24"x12"	0'-10½"	1,496 CFM	748 FPM
1245847	L2	24"x12"	4'-3"	1,496 CFM	748 FPM
1245849	L2	12"x24"	16'-10" (vertical riser)	1,496 CFM	748 FPM

Round branches, 8"ø ("Taps / Short Radius")

Ids	Level	Length (each)	Flow (each)	Velocity
1245552	L2	18'-9⅜"	226 CFM	648 FPM
1245564, 573, 582, 591, 600, 610, 619, 628 (8 ducts)	L2	18'-1⅜"	500 CFM	1,432 FPM
1245561, 570, 579, 588, 597, 607, 616, 625 (8 ducts)	L1	1'-7⅛" (short drops)	500 CFM	1,432 FPM

By level, 13 ducts are on L2 and 8 are on L1. The 91 ft main (1245546) and one branch (1245607) are on the system's critical path.

The 8" branches carrying 500 CFM run at about 1,430 FPM. That is on the high side for low-pressure branch duct, so they may be worth checking if noise matters. I can select or zoom to any of these in Revit, or export the list to a spreadsheet.