HVAC Drafting Basics: A Beginner’s Guide for HVAC Draftsman

 

HVAC Drafting Basics: A Beginner’s Guide for HVAC Draftsmen

In modern building construction, HVAC shop drawings are a critical part of the MEP (Mechanical, Electrical, and Plumbing) workflow. Whether you're just starting your career or transitioning into HVAC drafting, understanding the shop drawing process is essential. This guide will walk you through the fundamentals of HVAC drafting and help you confidently begin your first shop drawing.

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1. Understanding HVAC Systems

HVAC stands for Heating, Ventilation, and Air Conditioning. It’s a system that maintains indoor air quality and thermal comfort. As a draftsman, you should understand basic HVAC system types like:

• DX (Direct Expansion) Systems
• Chilled Water Systems
• VRF (Variable Refrigerant Flow) Systems
• Split AC or Package Units

Key components to represent in your drawings include:

• AHUs (Air Handling Units)
• FCUs (Fan Coil Units)
• Ducts
• Diffusers & Grilles
• Dampers & Access Doors

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2. What is a Shop Drawing?

A shop drawing is a detailed construction-level drawing that shows how HVAC systems will be fabricated and installed on-site. Unlike design drawings, which show the intent, shop drawings are meant for execution.

Stakeholders using shop drawings include:

• Site installation teams
• Project engineers
• Consultants
• Fabricators

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3. Tools and Software Required

To begin HVAC drafting, you’ll need the right tools:

• AutoCAD (2D drafting) or Revit (BIM modeling)
• Duct sizing calculators (manual charts or Excel-based tools)
• PDF editor/viewer for reviewing drawings
• HVAC symbol libraries for AutoCAD or Revit

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4. Collecting Project Data Before Drafting

Before starting the drawing:

🔍 Study HVAC Design Drawings and Schematics

Before starting any HVAC shop drawing, the very first step is to thoroughly study the HVAC design documents provided by the consultant or designer. These drawings serve as the blueprint for your shop drawings and provide all the necessary technical guidance.

Here's what to look for:

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✅ 1. HVAC Layout Plan (Design Drawings)

This plan shows:

·         The duct routing for supply air (SA), return air (RA), and exhaust air (EA)

·         The locations of equipment such as AHUs, FCUs, VAVs, and exhaust fans

·         The diffuser and grille placement in each room or space

·         Symbols or abbreviations that represent each component

👉 As a draftsman, your job is to convert this schematic-level routing into an installation-ready, dimensioned, and coordinated shop drawing.

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✅ 2. HVAC Schematic Diagrams

These diagrams show the airflow or piping connections between major components, including:

·         AHU → VCD → Duct → Diffusers → Return Duct → AHU

·         Chilled water lines connecting chillers, pumps, and coils (if applicable)

They help you understand:

·         The sequence of equipment

·         How each system is interconnected

·         Control valve locations (for BMS or manual control)

🧠 Tip: Use the schematic to visualize system logic before starting the layout. It helps you ensure your ducting matches the intended design sequence.

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✅ 3. Airflow Quantities and Duct Sizes

Check each outlet and duct segment for:

·         CFM (Cubic Feet per Minute) values

·         Duct sizes and velocity limitations

·         Balancing damper positions (usually placed near branch lines)

📏 This data is used to verify or calculate duct sizes using SMACNA guidelines or duct sizing software/spreadsheets.

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✅ 4. Notes and Legends

Design drawings usually contain:

·         A symbol legend (for AHU, FCU, Diffuser, etc.)

·         General notes like installation instructions, insulation requirements, fire rating, etc.

·         Abbreviations (SA, RA, EA, VCD, VAV, etc.)

Always keep the legend nearby so you don’t misinterpret symbols during drafting.

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✅ 5. Cross-reference with Other Drawings

Before you draft:

·         Check architectural floor plans to align your ducts correctly

·         Review RCP (Reflected Ceiling Plans) to see if ducts will fit above the ceiling

·         Coordinate with other services (plumbing, electrical) to avoid conflicts

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📌 Summary:

Studying HVAC design drawings and schematics is essential because:

·         It sets the foundation for accurate shop drawings

·         Prevents costly mistakes during installation

·         Helps you understand how the system works

Take your time with this step. A clear understanding at the start will save hours of rework later.

 

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🏢 Understand the Architectural Floor Plan and Reflected Ceiling Plan (RCP)

Before you begin drafting HVAC shop drawings, it's critical to study the architectural floor plan and reflected ceiling plan (RCP). These drawings are the skeleton of the building and directly impact how and where you route your ducts, place diffusers, and install equipment.

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✅ 1. Architectural Floor Plan

This drawing provides a top-down view of the building layout, showing:

·         Room dimensions and shapes

·         Wall thicknesses and materials

·         Doors, windows, and partitions

·         Staircases, shafts, and service areas

Understanding the floor plan helps you:

·         Determine where ducts can be routed without clashing with walls

·         Identify vertical shafts or risers for duct drops

·         Plan the placement of AHUs, FCUs, and other equipment in designated mechanical rooms

·         Check floor-to-floor heights or slab thicknesses that may affect duct space

🔍 Key Tip: Always verify if any rooms are double-height or have sloped ceilings—this affects duct elevation and placement.

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✅ 2. Reflected Ceiling Plan (RCP)

The RCP is essentially a mirror view of the ceiling, showing:

·         Ceiling types (gypsum, metal, tile grid, etc.)

·         Ceiling levels and height variations

·         Lighting fixtures, access panels, sprinklers, and smoke detectors

·         Ceiling-mounted diffusers, grilles, or cassettes

This plan is crucial because it tells you:

·         How much clearance space you have above the ceiling for ducts

·         Where you can safely place supply and return outlets

·         Which ceiling zones are service-free (e.g., above decorative ceilings)

·         Where coordination is needed to avoid clashes with lighting, plumbing, or fire sprinklers

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✅ 3. Why Coordination with Floor Plan and RCP Matters

·         Prevents ducts from running into beams, walls, or columns

·         Ensures aesthetic alignment of ceiling-mounted components

·         Allows for smooth installation with minimal revisions

·         Helps in preparing builder’s work drawings (for slab openings or duct sleeves)

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📎 Example:

Let’s say you need to place a supply diffuser in a meeting room. The floor plan tells you where the walls and doors are, and the RCP tells you:

·         What type of ceiling is above

·         Where the lights are installed

·         If there’s a coffer or bulkhead that limits space

Only when you study both drawings together can you confidently decide where to run your ducts and place the diffuser.

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📌 Summary:

Understanding architectural floor plans and RCPs ensures your HVAC layout:

·         Fits physically

·         Looks clean

·         Meets design intent

·         Avoids costly site rework

Always overlay these drawings into your AutoCAD or Revit model using Xrefs or underlays for seamless coordination.

📄 Look for Builder Work Drawings and Coordination Requirements

Before you start detailing your HVAC shop drawing, it's important to review builder work drawings and understand the coordination requirements with other trades. These documents help ensure your ducts and equipment will physically fit into the building and that they won't clash with other services like plumbing, electrical, and fire protection systems.

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✅ 1. What Are Builder Work Drawings?

Builder work drawings are detailed sketches that show:

·         Openings in walls, floors, and ceilings for ducts, pipes, and conduits

·         Sleeves, blockouts, and embedded items to be provided by civil or structural teams

·         Exact locations and sizes of all penetrations required for HVAC, electrical, and plumbing services

🔧 These drawings are typically submitted early in the project so the structural team can provide cutouts before casting concrete or building masonry walls.

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📌 Why Builder Work Drawings Matter for HVAC

If you don’t properly coordinate your ductwork openings with the structure:

·         Ducts may not pass through slab or beam due to missing or undersized openings

·         Additional site work (cutting, breaking) will be required, delaying the project

·         Coordination issues will arise during inspection or commissioning

🧠 Tip: Always prepare builder work drawings for all floor slab penetrations, wall sleeves, and large duct risers based on your shop drawing.

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✅ 2. Coordination Requirements

In an MEP project, HVAC must be carefully coordinated with:

·         Plumbing: Drainage pipes, water supply lines

·         Electrical: Cable trays, conduits, lighting fixtures

·         Fire Fighting: Sprinkler pipes, valves, fire alarm devices

·         Structure: Beams, columns, slabs, ceilings

💡 To avoid conflicts:

·         Use Xrefs (External References) to overlay all service layouts in AutoCAD

·         Attend coordination meetings with other trades

·         Follow vertical and horizontal coordination zones (often defined in BIM Execution Plans)

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🔍 Check for:

Coordination Item	Details to Look For
Slab openings	Location, size, and height from FFL
Wall penetrations	Are sleeves needed for insulated ducts?
Duct height clearance	Is there enough space above ceiling?
Service clashes	Are any ducts overlapping pipes or lights?
Access requirements	Is access provided for dampers and filters?

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📌 Summary:

Builder work drawings and coordination are the backbone of accurate shop drawings. They help you:

·         Ensure ducts and equipment fit as planned

·         Avoid costly changes during construction

·         Keep the project on schedule and compliant

Always request the latest builder work details from the civil/structural team and update your HVAC shop drawing accordingly.

📏 Note Ceiling Levels and Service Spaces

Understanding ceiling levels and the available service space above the ceiling is a crucial step before you begin routing ducts in your HVAC shop drawing. If overlooked, it can lead to serious coordination issues, installation delays, and expensive rework on-site.

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✅ 1. What Are Ceiling Levels?

Ceiling levels refer to the finished ceiling height in each room or zone. They are usually shown in the Reflected Ceiling Plan (RCP) or in elevation drawings.

For example:

·         Office Area: Ceiling at 2700 mm

·         Corridor: Ceiling at 2500 mm

·         Lobby: Ceiling at 3000 mm

Each space may have different ceiling heights, especially in hotels, hospitals, malls, or commercial buildings.

🧠 As a draftsman, you must be aware of these levels because they directly affect:

·         Where ducts can be routed

·         How deep duct drops can go

·         Whether certain equipment can be concealed

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✅ 2. What Is Service Space?

Service space is the clear height available above the ceiling (also known as the plenum space) where all MEP services run — including:

·         HVAC ducts

·         Electrical conduits and cable trays

·         Plumbing and drainage pipes

·         Fire sprinkler systems

📏 For example:

·         Structural floor-to-floor height: 3500 mm

·         Finished ceiling: 2700 mm
➡ Available service space: 800 mm

You must fit your ducts, insulation, and supports within this height, along with other services.

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🧱 Consider Structural and Architectural Constraints

When analyzing ceiling levels, always check:

·         Beam depths that may limit duct routing

·         Bulkheads or false ceilings that may interrupt continuous duct runs

·         Slab drops or slab openings in riser areas

·         Column positions and how they affect duct paths

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🔍 How to Verify Ceiling & Service Spaces:

Source	What to Look For
Reflected Ceiling Plan (RCP)	Ceiling types and heights
Section or Elevation Drawings	Beam depths and clearances
Architectural General Notes	Special zones with low ceilings
Coordination Drawings	Clash zones and congested areas
BIM Model (if available)	3D visual space checks

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📎 Example:

Let’s say you’re running a 500 mm x 300 mm supply duct with 50 mm insulation, and you also need 100 mm for hangers and support.

That means:

·         Total vertical space needed = 300 + 50 + 100 = 450 mm

If your plenum space is only 400 mm, this duct won't fit unless:

·         You reduce duct size or change routing

·         Request ceiling height adjustment

·         Switch to a flat oval duct or redesign the system

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📌 Summary:

Always note the ceiling levels and available service space before finalizing your duct layout. This will help you:

·         Avoid clashes during installation

·         Keep services concealed as per design

·         Maintain correct duct slopes, sizes, and insulation clearance

Proper planning here leads to a clean, coordinated, and constructible HVAC system.

5. Preparing the Drawing Template

Setup your workspace in AutoCAD:

• Use a company-standard title block

• Organize layers for supply air, return air, exhaust, insulation, etc.

• Set the correct drawing scale (e.g., 1:50 or 1:100)

• Use industry standards like SMACNA or ASHRAE

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6. Starting the Shop Drawing

Now begin your drawing:

• Trace duct runs starting from AHUs or FCUs

• Show duct routing with all bends, branches, and accessories

• Add diffusers, grilles, and air outlets

• Include dimensions, elevations, and duct sizes

• Use proper annotations and tags

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7. Coordination with Other Services

HVAC systems often overlap with electrical conduits, plumbing lines, or fire-fighting pipes. Good coordination helps avoid clashes.

• Use Xrefs (external references) to overlay drawings

• Highlight each service using different color codes

• Adjust duct routes to avoid beams and structural elements

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8. Quality Checks Before Submission

Before submission:

• Run purge and audit in AutoCAD

• Confirm all items are labeled and dimensioned

• Ensure all symbols and legends are present

• Drawings should match BOQ (if applicable)

• Double-check sheet size, title block, and north direction

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9. Submission & Revision Process

Export drawings as PDF:

• Submit for consultant/engineer approval

• Await review comments or redlines

• Revise accordingly and update drawing records

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🧠 Conclusion

HVAC drafting is both a technical and visual skill. With practice, attention to detail, and proper tools, you’ll become proficient in creating professional shop drawings. Always follow the latest project standards, and don’t hesitate to ask questions or seek clarification from engineers or senior draftsmen.