What Makes Industrial Duct Different from HVAC Duct?
Standard HVAC flexible duct is designed for conditioned air at 0-60°C (32-140°F) with no chemical exposure. Industrial flexible duct must handle extreme conditions that would destroy standard HVAC duct within hours:
- Temperature: Up to 400°C (750°F) for welding and exhaust applications
- Chemical resistance: Acids, solvents, oils, and corrosive fumes
- Abrasion: Dust, particles, wood chips, and metal shavings passing through the duct
- Negative pressure: Industrial exhaust systems operate under significant suction — duct must resist collapse
- Outdoor exposure: UV, rain, and temperature cycling for outdoor installations
Types of Industrial Flexible Duct
High-Temperature Flexible Duct
Designed for exhaust systems handling hot air, engine exhaust, welding fumes, and oven/furnace ventilation. Made from materials like silicone-coated fiberglass, stainless steel, or ceramic fiber. Temperature ratings range from 200°C (400°F) for silicone-coated models to 650°C (1,200°F) for ceramic fiber types.
Common applications: welding fume extraction, engine test cell exhaust, industrial oven exhaust, boiler room ventilation, generator exhaust routing, and foundry ventilation.
Chemical-Resistant Flexible Duct
Built from PVC, PTFE (Teflon), or polyurethane with chemical-resistant wire reinforcement. These ducts handle corrosive fumes from chemical processing, plating operations, laboratory exhaust, and pharmaceutical manufacturing. Chemical compatibility must be verified for each specific application — no single material resists all chemicals.
Heavy-Duty Abrasion-Resistant Duct
Designed for material transport: wood dust collection, sandblasting exhaust, grain handling, and metal chip extraction. These ducts use thick polyurethane or rubber walls (typically 0.6-1.5 mm) with embedded steel wire helix. The wall thickness is 3-5× that of standard HVAC flex duct to resist abrasive wear from particles traveling at 2,000-4,000 fpm.
Underground / Confined Space Ventilation Duct
Lightweight, collapsible duct used for temporary ventilation in mines, tunnels, construction sites, and confined spaces. Typically made from reinforced PVC or polyester fabric. These ducts must be flame-retardant (often to MSHA standards for mining), anti-static (to prevent dust ignition), and lightweight enough for manual handling in tight spaces.
Material Comparison
| Material | Max Temp | Chemical Resistance | Abrasion Resistance | Weight | Cost Level |
|---|---|---|---|---|---|
| Aluminum (standard) | 200°C (400°F) | Poor | Low | Light | $ |
| PVC (reinforced) | 60°C (140°F) | Good (acids, bases) | Medium | Medium | $ |
| Polyurethane | 90°C (200°F) | Good | Excellent | Medium | $$ |
| Silicone-coated fiberglass | 300°C (570°F) | Excellent | Low | Light | $$ |
| Stainless steel (corrugated) | 400°C (750°F) | Excellent | High | Heavy | $$$ |
| PTFE (Teflon) | 260°C (500°F) | Outstanding | Medium | Light | $$$$ |
| Ceramic fiber | 650°C (1,200°F) | Good | Low | Medium | $$$ |
Sizing for Industrial Applications
Industrial duct sizing follows different rules than HVAC because the primary concern is capture velocity (the speed needed to capture contaminants at the source) rather than room comfort.
| Application | Required Capture Velocity | Typical Duct Size | Transport Velocity |
|---|---|---|---|
| Welding fumes | 100-150 fpm at hood | 4"–8" | 2,000 fpm min |
| Grinding / buffing dust | 200-500 fpm at hood | 4"–6" | 3,500 fpm min |
| Wood dust collection | 200-500 fpm at hood | 4"–12" | 3,500–4,000 fpm |
| Chemical fume hoods | 80-120 fpm face velocity | 6"–10" | 1,500 fpm min |
| Paint spray booths | 100-150 fpm | 12"–24" | 2,000 fpm min |
| Grain / material handling | 200-500 fpm | 6"–16" | 3,000–4,500 fpm |
Transport velocity — the speed inside the duct — must be high enough to keep particles airborne and prevent settling. If particles settle in the duct, they create blockages, fire hazards (for combustible dusts), and eventually destroy the duct through abrasion at the settled layer.
Installation Considerations for Industrial Duct
Grounding and static dissipation. Combustible dust (wood, grain, metal powder, pharmaceutical) requires static-dissipative or grounded duct to prevent static discharge ignition. NFPA 652 mandates bonding and grounding of all duct components in combustible dust environments. Use duct with embedded ground wire and connect it to the facility's grounding system at both ends.
Support spacing. Industrial duct carries more weight than HVAC duct (heavier materials, collected particles) and operates under higher negative pressure. Support every 3-4 feet for horizontal runs. Use saddle supports, not wire hangers — wire cuts into the duct wall under load.
Bend radius. Maintain a minimum centerline bend radius of 2× the duct diameter. Tight bends cause particle buildup, increased pressure drop, and accelerated wear on the outer wall of the bend.
Inspection access. Install clean-out ports at low points, bends, and every 20 feet of straight run. Industrial duct accumulates material that must be periodically removed to maintain airflow and prevent fire hazards.
Industrial Flexible Duct Applications by Industry
The versatility of industrial flexible duct means it serves dozens of industries. Here are the most common applications, organized by sector:
Manufacturing & Metalworking
- Welding fume extraction: 4"-8" silicone-coated or stainless steel duct rated to 300-400°C, connected to portable or fixed extraction arms. OSHA PEL for welding fumes is 5 mg/m3 -- proper duct sizing ensures adequate capture velocity at the weld point.
- Grinding and polishing: Heavy-duty polyurethane duct (0.9-1.5 mm wall) for metal dust and particles. Transport velocity must exceed 3,500 fpm to prevent settling.
- CNC machine exhaust: 4"-6" duct for mist collectors and coolant fume extraction. PVC or polyurethane resists oil and coolant exposure.
Woodworking & Furniture
- Dust collection systems: 4"-12" anti-static polyurethane duct is the industry standard. Wood dust is combustible (NFPA 652 Class ST1), so all duct must be grounded. Static buildup in ungrounded PVC duct has caused workshop fires.
- CNC router exhaust: Large 8"-12" duct for high-volume chip extraction at 4,000+ fpm transport velocity.
Food Processing & Pharmaceuticals
- Cleanroom ventilation: PTFE or FDA-grade silicone duct that can be autoclaved. Zero-porosity walls prevent contamination.
- Ingredient handling: Polyurethane duct for pneumatic conveying of powders, granules, and pellets. Anti-static grounding prevents dust explosion risk per NFPA 652.
- Oven exhaust: High-temperature duct (200-300°C) for bakery and cooking process exhaust.
Construction & Mining
- Confined space ventilation: Lightweight 12"-24" PVC or polyester fabric duct, flame-retardant to MSHA standards. Must deliver 200+ CFM per occupant per OSHA 29 CFR 1926.353.
- Tunnel ventilation: Large-diameter (24"-48") reinforced duct for fresh air supply during tunnel boring and underground construction.
How to Choose the Right Industrial Flexible Duct
Selecting industrial flexible duct requires matching four critical parameters to your application:
- Temperature: What is the maximum continuous operating temperature? Add a 50°C safety margin above your peak temperature. A 250°C exhaust needs duct rated to at least 300°C.
- Chemical exposure: What gases, vapors, or liquids will contact the duct interior? No single material resists all chemicals -- verify compatibility with your specific substances. PTFE offers the broadest chemical resistance but at the highest cost.
- Abrasion level: Are particles, chips, or granules passing through the duct? If yes, wall thickness matters more than material type. Minimum 0.6 mm wall for light abrasion, 1.0+ mm for heavy material transport.
- Diameter and airflow: Size duct by CFM requirement and transport velocity, not by the equipment outlet size. Undersized duct causes excessive pressure drop and reduced capture efficiency.
Sourcing Industrial Flexible Duct
USFlexDuct manufactures industrial flexible hoses and duct from 1" to 48" diameter for temperature ranges up to 400°C. Our Houston, TX warehouse stocks common sizes for same-week shipping across the continental US. Custom diameters, materials, and lengths are available with 15-25 day lead time from our production facility.
Our industrial product line includes high-temperature exhaust duct, chemical-resistant PVC duct, heavy-duty polyurethane material handling hose, and underground ventilation duct. All products meet relevant UL, MSHA, and OSHA standards for their rated applications.