Industrial ductwork isn’t one-size-fits-all. The right material depends on corrosion risk, temperature, pressure, cleanliness requirements, fire code, noise control, and budget.
Galvanized steel duct
- Galvanized steel duct: The industry workhorse for supply, return, and exhaust systems.
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- Pros: Durable; relatively low cost; good structural strength; widely available; easy to form and join.
- Cons: Can corrode in highly corrosive or humid/chemical environments; heavier than aluminum.
- Best for: General industrial HVAC, warehouses, manufacturing floors.
- Joining/sealing: Flanged or spiral-lock seams; use mastic or UL-approved foil-backed tape; gasketed flanges for higher-pressure runs.
- Maintenance note: Inspect for surface rust in corrosive environments and touch-up/replace as needed.
Stainless steel duct
- Stainless steel duct: Corrosion-resistant option for aggressive environments.
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- Pros: Excellent corrosion resistance; sanitary (good for food, pharma); long lifespan.
- Cons: Higher material and fabrication cost; heavier than aluminum per strength ratio.
- Best for: Corrosive environments, chemical plants, food processing, pharmaceutical, high-humidity spaces.
- Joining/sealing: Welds or flanged connections; compatible with sanitary clamps; use silicone gaskets for food-grade systems.
- Maintenance note: Minimal surface treatment required, but check for pitting in chloride-rich atmospheres.
Aluminum duct
- Aluminum duct: Lightweight and corrosion-resistant alternative to steel.
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- Pros: Lighter (easier handling/installation); naturally corrosion resistant; good for long unsupported spans.
- Cons: Softer than steel (can dent); typically more expensive than galvanized steel but cheaper than stainless in many cases.
- Best for: Roof-level ducts, outdoor ducts, coastal facilities where salt exposure exists but stainless isn’t required.
- Joining/sealing: Rivets and continuous sealant or specialized aluminum flanges; closed-seam spiral options available.
- Maintenance note: Inspect for galvanic corrosion where aluminum contacts dissimilar metals.
Lined or insulated sheet metal (double-wall / lined ducts)
- Lined or insulated duct systems: Metal duct with internal insulation or double-wall construction for noise and thermal control.
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- Pros: Adds thermal insulation and sound attenuation; can reduce condensation; cleaner interior when properly specified.
- Cons: Insulation must be selected for fire code (non-combustible options available); internal liners can collect dust if not maintained.
- Best for: Conditioned process areas, HVAC serving occupied spaces requiring noise control, chilled systems prone to condensation.
- Joining/sealing: Use vapor-barrier seals on joints; maintain continuous vapor barrier where needed.
- Maintenance note: Inspect liners for moisture and microbial growth; replace if contaminated.
Fiberglass duct board
- Fiberglass duct board: Preformed insulating board used for low-pressure ductwork.
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- Pros: Built-in insulation and sound control; quick to install in some retrofits; lightweight.
- Cons: Not ideal for high-velocity/high-pressure or oily/greasy environments; edges must be sealed properly; some codes restrict use in certain commercial/industrial applications.
- Best for: Low-pressure return ducts in non-contaminating environments or budget-sensitive projects.
- Maintenance note: Protect from mechanical damage and moisture; consider encapsulated alternatives for hygiene.
Fabric (textile) ductwork
- Fabric / textile ducts: Perforated fabric tubing used for uniform air distribution.
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- Pros: Excellent air distribution and fast installation; lightweight and can be launderable; reduces drafts.
- Cons: Not suitable where physical damage, high temperatures, or contaminant exposure are risks; limited for high-pressure systems.
- Best for: Large open industrial spaces (warehouses) where gentle distribution and quick installation are priorities.
- Maintenance note: Regular cleaning or replacement cycles depending on contaminants.
How to choose the right material:
- Environment: Corrosive (choose stainless/aluminum) vs. dry/neutral (galvanized is fine).
- Temperature & pressure: High temps or high static pressures favor welded stainless or heavy-gauge steel.
- Cleanliness & sanitation: Food, pharma, or clean rooms: stainless + sanitary fabrication.
- Noise / thermal control needs: Use lined/double-wall ducts or add external insulation where needed.
- Mechanical abuse risk: In high-traffic or impact areas, use heavy-gauge metal and protective routing.
- Budget & lifecycle cost: Consider long-term replacement and maintenance costs, not just upfront price.
- Code & standards compliance: Follow local codes and industry standards (SMACNA practices, NFPA where fire-rated systems are required).
- Installation logistics: Weight, handling, and available fabrication skill affect material choice.
Installation best practices
- Proper sealing: Use UL-approved sealants, mastic, or foil tapes for low-leak systems; gasketed/flanged joints for higher pressure.
- Support & hangers: Follow manufacturer spacing limits; allow for thermal expansion and avoid sagging.
- Corrosion protection: For exterior or corrosive environments, coat or choose corrosion-resistant alloys.
- Insulation & vapor barriers: On chilled systems, maintain continuous vapor barriers to prevent condensation and mold.
- Access & maintenance: Install access doors at equipment, filters, and cleanable bends.
- Fire & smoke considerations: If required, specify fire-resistant lining, smoke dampers, and proper penetration seals.
- Testing after install: Perform duct leakage tests (e.g., blower door/duct pressurization), airflow balancing, and static pressure verification.
Cost considerations
- Lowest upfront: Galvanized sheet metal (common).
- Moderate: Aluminum and lined/insulated systems.
- Highest upfront: Stainless steel (but lowest replacement in corrosive situations).
- Value tip: If corrosion or sanitation will force frequent replacement, invest more up front (stainless or proper coatings) — total lifecycle cost is often lower.
On sealing, joining, and fasteners: practical tips
- Use mechanical fasteners plus continuous sealant for long-term leak control.
- For spiral ducts, use continuous sealed spiral joints with mastic on the seam.
- For welded stainless ducts, tests for leak tightness and cleanliness before startup.
- Avoid relying solely on tapes that aren’t rated for HVAC use. Choose UL/ASTM-rated materials.