The Workhorse Diameter Range
DN250 to DN600 is where most industrial ventilation systems live. This is the zone header collecting from multiple branch drops. The main exhaust trunk running along the factory wall. The scrubber inlet duct. The fan discharge stack. These diameters handle the airflow volumes that matter — 2,000 to 28,000 m3/h at standard transport velocities — and the engineering decisions made here determine whether the system runs efficiently for 15 years or becomes a maintenance burden.
All diameters in this range are produced by one-piece injection molding — no longitudinal weld, no spiral seam. At DN600, this is near the upper limit of most manufacturers’ injection molding capability. Our tooling handles it as a standard production diameter. See our PP Round Duct main product page for full specifications.
DN250-DN600 Sizing Reference
| DN | Airflow at 10 m/s | Airflow at 14 m/s | Typical Application |
|---|---|---|---|
| DN250 | 1,770 m3/h | 2,470 m3/h | Small zone header (3-5 hoods), single process equipment exhaust, tank vent manifold |
| DN315 | 2,800 m3/h | 3,900 m3/h | Medium lab zone (8-12 hoods), dust collector main, plating line exhaust lateral |
| DN355 | 3,560 m3/h | 4,980 m3/h | Building riser (single floor), scrubber inlet for 5,000 m3/h system |
| DN400 | 4,520 m3/h | 6,330 m3/h | Main exhaust trunk (small factory), multiple scrubber manifold, paint booth extraction main |
| DN450 | 5,720 m3/h | 8,010 m3/h | Chemical plant process exhaust main, pharmaceutical building riser |
| DN500 | 7,060 m3/h | 9,890 m3/h | Factory main exhaust, central scrubber inlet, multi-floor building riser |
| DN600 | 10,170 m3/h | 14,240 m3/h | Large factory main, single central scrubber, semiconductor fab sub-fab exhaust main |
These are single-duct capacities. For higher air volumes, multiple parallel ducts or step up to larger diameters. For DN600 and above, see our Round Duct DN600-DN1000 and DN1000-DN1500 pages.
Why the Middle Range Demands the Best Quality
Small-diameter duct (DN15-DN200) is forgiving — short spans, low weight, easily supported, low consequence if a section needs replacement. Large-diameter duct (above DN600) is inherently robust — wall thickness of 8-12 mm provides structural margin. The middle range is where manufacturing quality has the most impact:
- Wall thickness consistency matters. At DN400 with 5 mm wall, a 10% under-thickness is 0.5 mm — seemingly minor, but it reduces the vacuum rating of that section by roughly 10%. If your system operates at -500 Pa and the duct is specified for -600 Pa with a 20% safety factor, a 10% under-thickness section drops the safety factor to 10%. Still within spec, but with half the margin the designer intended.
- Out-of-round affects flange sealing. At DN250-DN600, flange connections are common at equipment interfaces and access points. An out-of-round duct end — even a few millimeters — creates uneven gasket compression at the flange joint. The high spot compresses fully; the low spot barely touches. The joint leaks at the low spot. Injection-molded duct maintains circularity that hand-fabricated duct cannot match.
- Support spacing directly impacts sag. PP duct spans between supports must be calculated for the material’s modulus at operating temperature. At 40degC, PP’s modulus is approximately 70% of its room-temperature value. Support spacing that works at 20degC may allow unacceptable sag at 40degC. For DN250-DN600, typical support spacing is 2-3 meters depending on diameter, wall thickness, and operating temperature. We provide support spacing recommendations with every duct order. Industrial ventilation duct design follows principles consistent with OSHA 29 CFR 1910.94 Ventilation requirements for exhaust systems handling chemical contaminants, which specify that ductwork must maintain structural integrity under the full range of operating temperatures and pressures.
Common Configurations in the DN250-DN600 Range
- Zone collection header. Multiple DN150-DN200 branch drops from individual hoods or equipment connections feeding into a DN315-DN400 zone header running along the wall or ceiling. The header diameter increases as each branch enters — a DN315 section after 4 branches may step up to DN355 after 8, and to DN400 after 12. See our PP Duct Reducer for diameter transitions.
- Scrubber-fan-duct package. A matched system: DN315-DN500 duct from the process to the scrubber inlet, scrubber, DN400-DN600 duct from scrubber outlet to fan inlet, fan, DN400-DN600 stack to atmosphere. We supply the complete package — duct + fittings + scrubber + fan — sized as one system with one warranty. See Wet Scrubber System.
- Multi-floor riser. A vertical DN315-DN500 duct running through multiple floors, with DN150-DN200 lateral take-offs at each floor via tee fittings. The riser diameter is constant (simplest) or stepped (most efficient) as floors are added. See our PP Duct Tee for branch connections.
Send your duct layout and airflow requirements to xicheng023@outlook.com. We’ll verify diameters, calculate pressure drop, and provide a complete quotation. WhatsApp: +86 18927456906.
