Last updated July 27, 2026
HVAC Suite is a set of nine dialog-driven AutoLISP programs for drawing 2D double-line ductwork in AutoCAD. It was written in 1996 by Matthew Volkar of V.C. Custom Programming, and every one of the nine tools — straight duct, tees and wyes, transformations, elbows, sections, branches, components, diffusers and dampers — works from a dialog box rather than a string of command-line prompts.
The suite dates from the Release 12 and 13 era, so treat it accordingly. Mechanical services drafters still producing 2D duct layouts may get direct use out of it, and it is also a worthwhile study of how a polished dialog-based LISP suite was put together in the mid-1990s. Read the licensing notes below before you build a workflow around it, though — this is shareware with a built-in run limit.
What it does in practice
The core tool, DDHVD, draws double-line duct relative to the centreline, the left side, the right side or an offset line. Options cover a visible centreline, interior or exterior insulation, dimensions and elevations. Dimensions are always placed in the centre of the duct and elevations at either end. Insulation is shown as a dashed line around the outside of the duct for exterior insulation, and around the inside for interior.
The remaining tools handle fittings and symbols. Tees and wyes can have symmetric or asymmetric outlets (wyes must be symmetrical) with options for turning vanes, a dividing sheet and insulation. Transformations are drawn by angle or by length, with optional left or right offsets and visible 3 inch end collars. Elbows can be sharp or smooth, with collars and turning or splitter vanes. Duct sections use linetype to show whether a run is exposed (continuous) or obscured (dashed); supply ducts get a cross through the centre, return ducts a single slash, and the linetype of that mark indicates air-flow direction. Branches run rectangular to rectangular, round to round or rectangular to round, with a 45/90 or 45/45 entry and options for collars, dampers and extractors. Separate tools place component, diffuser and damper symbols, with damper heads shaped and lettered by damper type.
Layers, linetypes and text styles are customisable through plain-text configuration files supplied with each module. The component tool, DDHVC, ships with eight symbols and can be extended: add an “AUX” entry to its configuration file and it will load an AutoLISP function of that name. A sample AUX routine that draws a circle is included as a template.
Command reference
- DDHVD — double-line ductwork
- DDHVDTEE — duct tees and wyes
- DDHVDTRF — duct transformations and offsets
- DDHVDELB — duct elbows
- DDHVDSEC — duct sections
- DDHVDBRN — duct branches and takeoffs
- DDHVC — HVAC component symbols
- DDHVCDIF — diffuser symbols
- DDHVCDMP — damper symbols
A note on the section command: the readme text refers to it once as DDHVCSEC, but that is a typo. The module’s help file is titled “DDHVDSEC Command – HVAC Duct Sections” and its dialog carries the same name, so DDHVDSEC is the command you type.
How to load it
The download holds nine separate zip files, one per module, and each unzips on its own. A module folder contains the LSP program plus its DCL dialog file, slide library, configuration file and help file, so extract the modules you want and keep each set of files together where AutoCAD can find them. Load the LSP with APPLOAD, or add it to the Startup Suite so it loads with every drawing. If loading routines is new to you, the AutoLISP guide walks through the process.
Step-by-step usage
- Load the module’s LSP file, then type its command name — DDHVD for straight duct, for example.
- A dialog box opens with the options for that fitting. In DDHVDSEC the dialog offers Rectangular, Round and Flat oval duct types alongside the exposure and insulation settings.
- Set your options, close the dialog and place the symbol in the drawing.
- Where DDHVD asks for elevations, the readme is specific: they “should be entered in the form of feet and inches with no spaces (i.e., 5’11")”. The suite works in imperial units throughout.
The LSP files ship in AutoCAD’s protected (encrypted) format, so the exact prompt sequences cannot be listed from the code. Each module includes an .AHP help file that documents its command in full, and the readme covers all nine.
Compatibility notes
- Written for AutoCAD Release 12 and 13 — the author states all nine programs were tested under both.
- Full AutoCAD only. Every tool is DCL dialog based, and DCL is not available on AutoCAD LT even though LT gained AutoLISP in the 2024 release. See what runs on AutoCAD LT for the detail.
- This is 1996 shareware. Each program is limited to 50 executions, after which it refuses to run, and a nag screen reports how many runs you have used. The registration details in the readme are almost thirty years old, so treat the limit as a hard cap.
- The LSP files are protected, so the source cannot be viewed or edited.
Download
| Name: | HVAC Suite |
| Description: | A full suite of lisp routines and blocks for designing and drawing HVAC systems. |
| Type: | AutoCAD AutoLISP Routine |
| Author: | See files |
| File Size: | 636 Kb |
| Cost: | Free |
| Worked on: | AutoCAD |
| Download File: | HVAC Suite.zip |
Related routines
- Draw architectural walls — another double-line drawing tool, aimed at wall layouts.
- Door LISP routine — places doors in plan, a common companion task on services drawings.
- Structural steel shapes — another discipline-specific symbol-drawing suite.
More free routines are catalogued in the LISP routine library.