Bus Air Ducts: Types, Materials and How to Buy Wholesale

Air ducts sit between the air-handling unit and the cabin outlets. Typical layouts include:

• Roof ducts — on coaches and tour buses, long side ducts run above the window line and feed the roof AC louvers.
• Roof cavity ducts — on city buses, ducts are built into the interior roof structure.
• Side / floor ducts — feed under-seat or floor-level outlets.
• Dash and demister ducts — short ducts that direct airflow onto the windscreen.

For most bus fleets, ABS and PVC composite are the practical mainstream choices: light enough for body weight, resistant to the moisture inside the duct, and quick to cut or fill for custom runs.

Colour also matters more than many buyers expect. A duct that is close to the interior headliner colour looks factory-fitted and is easier to sell downstream; a mismatched grey duct in a warm-beige interior is an instant objection at resale. When you request a quote, mention the interior colour code or send a trim sample, and most suppliers will match the closest standard colour without extra tooling. Surface finish is the second visual detail: a smooth, low-gloss finish hides dust and finger marks better than a shiny one, and it photographs better in catalogues and on dealer lots.

Flame retardancy is a regulatory point that buyers should not skip. Bus interior materials in most export markets are expected to meet flammability standards, and the duct sits directly above passengers. Ask for the material grade and, where relevant, the flammability rating of the ABS or PVC compound. This is not a nice-to-have: it can be a customs or homologation issue in some markets, and it is very hard to retrofit after installation.

Most production bus ducts are vacuum-formed or thermoformed from extruded ABS sheet. The process starts with a male or female mould shaped to the roof or side profile of the vehicle. A heated sheet of ABS is drawn over the mould under vacuum, forming the hollow, ribbed channel, then trimmed, drilled for mounting points and fitted with brackets and outlet openings for the louvers.

Vacuum forming is popular because tooling is relatively inexpensive compared with injection moulding, which matters when a fleet operator needs a duct for a specific vehicle model in moderate volumes. The wall thickness is typically 2–4 mm depending on the section and the expected service load. Ribs and double-wall sections add stiffness where the duct spans long unsupported runs between roof bows, reducing sag and rattle.

For buyers, the practical implication is that the mould is the "key" to the part: once a supplier has the mould for a given vehicle model, repeat orders are fast and consistent. If a supplier does not have the mould, they either need to cut and join standard sections (a retrofit solution) or build a new mould, which adds cost and lead time. This is why cross-reference support matters: ask whether the duct you need is already in production for that model before you commit to tooling.

Air ducts are model-specific. Gather four things to speed up the quote:

Because a duct is long and slightly flexible, one OEM part number may cover several related models. OEM-grade ducts such as Air Duct 6700, 6608 and 6602G from Newsong are produced to match the original fitting and cross-reference against the relevant vehicle models.

Installing a replacement duct is usually a two-person job on a coach, because the duct is long and needs to be offered up to the roof without twisting. The typical steps are: remove the old duct and its fixings, clean and inspect the mounting surface for corrosion or previous damage, test-fit the new duct before applying any adhesive or sealant, then fix in place with the original or supplied brackets and re-fit the louvers and trim.

Two installation details cause most of the problems in the field. The first is sealing: where the duct meets the evaporator outlet and at each joint, a flexible seal prevents conditioned air from leaking into the roof cavity instead of reaching the cabin. Losing 10–20% of airflow to leaks is common on older installations and directly reduces cooling capacity while the compressor keeps working full load. The second is fixing torque: over-tightening screws into plastic bosses cracks them, and under-tightening lets the duct rattle on rough roads. Use the specified screws, and where a bracket spans two materials, add a small rubber washer to isolate vibration.

Maintenance is mostly inspection and cleaning. The interior of the duct accumulates dust, especially at the outlet openings, and a blocked duct makes the blower work harder and increases noise. An annual inspection that checks the seals, clears the outlet openings and confirms the brackets are tight keeps the system performing. On vehicles with roof-mounted units, check the drain and the duct joint after heavy rain, because a water leak into the headlining is easier to prevent than to repair.

Workshops see a small set of recurring duct-related complaints. Understanding what each symptom means shortens diagnosis:

• Weak airflow at the last rows — usually a leak or a partially blocked duct section, or a damper left closed. Check the joints first, then the outlet openings.
• Rattling or drumming noise — loose brackets, a cracked boss, or the duct vibrating against the roof panel. Tighten, add rubber isolation, or check for cracks.
• Whistling at speed — air escaping through a small gap or a poorly seated louver. Seal the gap and re-seat the louver.
• Condensation on the duct surface — insufficient insulation, usually on aluminium or poorly insulated sections; the duct surface falls below dew point.
• Water stains on the headliner — a joint leak or a blocked roof drain. Repair the seal and clear the drain before replacing trim.

For a distributor, these diagnostic patterns are worth sharing with customers because they reduce warranty call-backs. A duct that fails early is rarely a material failure; it is almost always an installation or sealing issue, and a short installation guide supplied with the part prevents most of it.

• Confirm material and colour match with the vehicle interior.
• Check mounting and cut-out dimensions, not just length.
• Send a photo or sample if retrofitting a non-stock model.
• Ask about export packing and container mix for long, fragile ducts.
• Confirm MOQ and lead time before ordering.

Air ducts are long and relatively expensive to transport, and a wrong fit wastes time and money. A supplier with OE-grade duct patterns and vehicle cross-reference keeps the process simple. Guangzhou Newsong Auto Parts Co., Ltd. supplies air ducts and the wider bus HVAC system — ducts, louvers, condensers, evaporators — with cross-reference support for Yutong, King Long, Golden Dragon, Higer, Zhongtong, Foton and BYD vehicles.

Air ducts are among the more fragile parts in a bus HVAC order, purely because of their length. A 3–4 metre duct has little stiffness in the middle, so if it is packed poorly it can arrive cracked, bowed or with broken mounting bosses. Reliable export packing starts with the duct supported over its full length: foam or cardboard cradles every 50–80 cm, corner protectors on the ends, and a sturdy carton or wooden frame depending on the length and weight. Do not rely on loose fill, which settles in transit.

Because ducts are long, they are often the item that decides the container plan. A 40-foot high-cube container can be filled with a mix of bus parts, and the ducts are usually loaded flat along the floor or along one wall, with lighter parts on top. If you are ordering ducts together with condensers, louvers, filters and other HVAC parts, a mixed-SKU container from a single supplier reduces freight cost per piece dramatically compared with shipping each category separately. Ask the supplier how the ducts will be stowed in the container and what the loading order is.

Lead times vary by whether the duct is a stocked pattern or needs a production run. Stock items can often ship within 7–15 days; a duct that needs moulding usually runs 20–40 days depending on the mould and the season. For distributors planning a seasonal pre-stock, ordering 6–8 weeks ahead of the peak cooling season is the safe practice, especially when sea freight to the destination port takes 20–40 days on top of production time.

Customs documentation for bus parts is routine for an experienced exporter: commercial invoice, packing list, bill of lading and, where requested, certificate of origin. Ducts are classified under the usual plastic-vehicle-parts headings, so an accurate material declaration (ABS vs PVC) in the commercial invoice avoids duty surprises at the destination.

To make the process concrete, here is a typical order flow for a regional distributor stocking bus HVAC spares:

Most distributors find the second order is faster than the first: the cross-reference file is already built, the moulds are confirmed, and the packing plan is proven. This is why a single supplier covering the whole bus HVAC range tends to compound in value over time.

• Bus Air Duct product range
• Bus AC Louvers
• Air Con & Parts
• Evaporator
• Condenser

Send us your part list, OE numbers or a photo of the unit you need. We quote within one business day.

This guide was prepared for B2B sourcing reference in October 2026. Product ranges, specifications and MOQ can change — confirm the current catalogue with us before ordering.