The first step in HVAC fabrication starts with detailed and accurate ductwork drawings and measurements. Next, the sheet metal is cut to the required dimensions, using the calculated dimensions and angles for each duct section. 

Forming the duct sections comes next, using a sheet metal brake or hand seamer to create bends in the sheet metal (for corners or offsets). After the sections are formed, the ductwork is assembled, securing joints with screws or rivets, snap-lock seams, or spot welding. Before installing the ductwork, each section is closely inspected for any gaps, loose connections, or sharp edges. A pressure test is sometimes used to ensure there are not any leaks. Once fabrication is complete and quality checks are done, the ductwork can be installed according to the HVAC system design and local building codes.

What Are The Methods of Duct Fabrication?

Each method of duct fabrication has advantages and is chosen based on factors such as material type, installation requirements, system design complexity, and project budget. HVAC projects often involve a combination of manual craftsmanship and automated precision for efficient and durable ductwork installations.

Here are some of the methods commonly used for duct fabrication:

Sheet metal ductwork fabrication

Hand cutting and folding: This is the traditional method where sheet metal (typically galvanized steel or aluminum) is measured, cut using tin snips or shears, and then folded into shape using manual bending tools and hammers.

Screwed or riveted assembly: Sections of sheet metal are cut to size and assembled by screwing or riveting together. This method requires precise measurement and alignment to ensure tight seams.

Automated cutting and folding: Modern fabrication shops use computer-controlled machines (CNC) for precise cutting and folding of sheet metal based on CAD drawings. This method is efficient and allows for complex designs with minimal human error.

Fiberglass duct board fabrication

Fiberglass duct board is a lightweight and insulated material used for ductwork, typically cut using special knives or saws designed for fiberglass. Pieces are assembled using special adhesives and tapes, ensuring airtight joints.

Flexible ductwork fabrication

Flexible ductwork is often manufactured in pre-formed sections by the supplier. Installation involves cutting to length and connecting to fittings or other duct sections. This method is straightforward and suitable for quick installations in spaces where rigid ductwork is impractical.

Ductile iron pipe fabrication

For larger HVAC systems or industrial applications, ductile iron pipes are used. Fabrication involves cutting the pipe to size using cutting tools or saws and then welding pieces together using welding techniques suitable for ductile iron.

PVC duct fabrication

PVC ducts are fabricated by heat forming sections to the required shape and then welding pieces together using PVC welding techniques. This method is commonly used for corrosive or chemical-resistant applications.

Duct insulation fabrication

Duct insulation is typically applied after duct fabrication, using insulation materials such as fiberglass or foam wrapped around the ductwork and secured using adhesive or mechanical fasteners. This step is especially important for thermal efficiency and condensation control.

How Are HVAC Ducts Made?

Since HVAC ducts are typically made from sheet metal, here is a detailed overview of how sheet metal HVAC ducts are typically made:

Material selection

The most common materials used are galvanized steel or aluminum sheets. The choice depends on factors such as cost, corrosion resistance, and structural requirements.

Fabrication process

Sheets of metal are cut to the required dimensions using various tools:

• Tin snips: Hand-held tools for straight cuts and small bends.
• Power shears: Electric or pneumatic tools for faster cutting of straight lines.
• Plasma cutter or laser cutter: Automated tools for precise cutting, especially for complex shapes or thick metals.

After cutting, the metal sheets are formed into the required shapes and sizes. Sheet metal brakes are used to create bends and folds in the metal, then hand seamers are used to manually bend and fold smaller sections. Roll forming machines are used to create cylindrical or curved duct sections.

Duct sections are assembled by joining the formed pieces together, and joints may be secured using screws and bolts, rivets, locking seams, or welding. Spot welding or continuous seam welding is used for airtight joints – but this process is less common due to its complexity.

Quality control

Throughout the fabrication process, quality checks are performed to ensure:

• Dimensions are accurate
• Joints are securely fastened
• Insulation (if needed) is applied correctly 
• Ducts meet HVAC system design specifications and local building codes

Installation

Once fabricated and inspected, ductwork is installed in buildings. Duct sections are connected to HVAC equipment (air handlers, vents, etc.) using appropriate connectors and seals, and then ducts are supported with hangers and bracing to prevent sagging and ensure stability.

What Is a Duct Fabricator?

A duct fabricator is a HVAC professional who specializes in the manufacturing and assembly of ductwork systems used in HVAC systems. Their primary role involves taking design specifications and blueprints and using various materials (such as sheet metal, fiberglass, or flexible materials) to fabricate ducts according to precise measurements and requirements.

A duct fabricator’s key responsibilities typically include reading blueprints and specifications to ensure accurate fabrication, material selection, cutting and shaping, assembly and welding, quality control, supporting HVAC installers, and safety compliance. Duct fabricators play a crucial role in the construction and maintenance of HVAC systems, ensuring that air distribution in buildings is efficient and meets design specifications. Their work requires precision, attention to detail, and proficiency with various fabrication techniques and materials.

HVAC Ductwork Management Software Solutions

BuildCentrix has created the web’s only 3D online assembly builder to make ordering custom ducts fast and easy for users and fabricators. Fittings can be highly customized to the way you manufacture, install and even sell duct and duct accessories. Instant pricing, weight, budgeted labor and seamless integration into the CAM software make it an essential tool for any HVAC contractor. 

Learn more and find out how to get a 30-day free trial for BuildCentrix.