DuctDraft AI · Intelligent HVAC Drafting Automation
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Convert HVAC Single-Line Drawings to Double-Line in Seconds — and Save Drafting Time

Reduce manual HVAC duct drafting time from hours to minutes. Upload your single-line HVAC DXF file and get a fully drafted double-line output — complete with duct walls, elbows, branch shoes, reducers, endcaps, layer-matched colors, and a detailed conversion report.

Layer names & duct type Auto detect ⌄
Upload DXF No file ⌄
Preview DXF, then click shaft location on the preview modal.
Reducer method One side left ⌄
Support settings Off ⌄
Without support
DXF preview

DXF preview

How It Works

From upload to a CAD-ready double-line drawing.

Watch How It Works

See the full single-line to double-line conversion in a 55-second walkthrough.

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Specify Duct Layers

Enter the layer names — for example, SA, RE, EA, or FA.

Select the duct type — for example, Round, Rectangular, or Chilled Water.

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Upload Your DXF

Select a clean single-line HVAC DXF file from your machine.

Select the shaft to set flow direction.

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Geometry Analysis

The engine traces centerlines, identifies connected runs, and groups them by service type.

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Duct Size Resolution

Text labels and leaders are matched to their corresponding duct runs to assign cross-section dimensions.

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Fitting Generation

Branch shoes, elbows, inline reducers, and endcaps are constructed at every connection point.

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Conversion Report

A structured summary shows every layer, run, fitting count, and any warnings before you download.

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Download the Output

Save the converted double-line DXF file — fully layered and ready to open in any CAD application.

Prepare Your Drawing for the Best Results

The converter performs best when your DXF follows clean, consistent drafting standards. A few minutes of preparation can prevent most conversion warnings.

Drawing Standards
  • DXF format is required.
  • Single-line duct centerlines only — no double-line input.
  • Use LINE or LWPOLYLINE entities; splines are not supported.
  • Remove overlapping or duplicate line segments before uploading.
  • Draft all single-line drawings in millimeters (mm).
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Layer Structure
  • Each duct service must be on its own dedicated layer.
  • Output geometry is placed on the same layer as the input, preserving your color assignments.
  • Layer names should include a recognizable service keyword: SA, RE, EA, FA, SUP, RETURN, EXHAUST, or FRESH.
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Size Labels & Leaders
  • Size text must be standard CAD TEXT or MTEXT entities — not embedded in blocks.
  • Place size labels close to the duct section they describe.
  • A leader line connecting the text to the duct centerline significantly improves size matching accuracy.
  • The leader arrowhead or tip should land directly on or adjacent to the duct line.
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Scale & Scope
  • Draft all HVAC geometry in millimeters (mm).
  • Architectural and structural geometry should remain on separate, clearly named layers.
  • Lock or freeze non-HVAC layers before exporting to DXF to keep the file clean.
  • Geometry inside Xrefs or block definitions may not be processed correctly.
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How Your Drawing Should Look

Prepare your DXF before conversion. Clean centerlines, clear layer names, and proper size labels help DuctDraft AI produce better results.

Architectural and structural geometry

Architectural and structural geometry

All architectural layers must be locked.

  • Architectural geometry — separate layer, clearly named.
  • Architectural layers — locked before DXF export.
  • Reflected ceiling layer — locked and excluded from conversion.
Clean single-line duct centerline drawing

Clean single-line geometry

Draw ducts as clean single-line center paths. Avoid duplicate, broken, or overlapping linework.

  • Use LINE or LWPOLYLINE entities
  • Keep endpoints connected
  • Remove messy duplicate geometry
Duct services separated by layer

Separate services by layer

Each duct service should be placed on its own clear layer, such as SA, RE, EX, or FA.

  • Supply air on SA or SUP layer
  • Return air on RE layer
  • Exhaust air on EX layer
Size labels connected to duct centerline with leaders

Size labels with leader pointer

Size text should be close to the duct and connected with a leader line. This improves automatic size matching.

  • Example: 500x400 or Ø250
  • Leader tip should touch the duct line
  • Use normal TEXT or MTEXT
Fire dampers

Fire & volume damper

Fire dampers are placed based on your input on the DWG.

  • Position the leader at the desired fire damper location.
  • A symbolic fire damper will be inserted automatically.
  • Replace the symbolic placeholder with the actual fire damper block once the drawing is finalized.
  • Volume dampers are placed on fresh air and supply duct branch
Company Template Settings page showing company information, default conversion settings, support settings, and quantity takeoff settings

Company standards template

Set your company's defaults once, and every conversion and quantity takeoff uses them automatically — no need to re-enter the same values on every run.

  • Company info, reducer method, and support option defaults
  • Support spacing, edge margin, branch clearance, and minimum run length
  • Sheet metal, insulation, labor, and unit cost rates for QTO

After Conversion — Review Before Issuing

AI-generated output can contain mistakes. Always have a qualified engineer or CAD team review and verify the drawing before it is released.

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Open in CAD

Open the downloaded DXF in AutoCAD or your preferred CAD application and visually scan each duct service layer.

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Check All Fittings

Inspect every branch shoe, elbow, reducer, and endcap. Confirm placements align with the original single-line intent.

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Verify Duct Sizes

Cross-reference generated duct widths against the original size annotations and leader notes in the source drawing.

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Drafter Sign-Off

Have a qualified CAD drafter perform a final QA review and apply any project-specific drafting standards before issue.

Contact us

Questions about a conversion, a plan, about drawing or report Send us a message.

Let's talk

We usually reply within a day. For anything urgent, reach out directly.

✉ support@ductdraftai.com
🕐 Mon–Fri, 9am–6pm EST