Print Sector HVAC Ductwork — Newspaper, Commercial, Publishing & Packaging

Why print sector HVAC is its own discipline

A print plant looks, from the outside, like a fairly standard light-industrial shed. Walk inside any heatset web offset newspaper press or any major sheetfed packaging printer and the mechanical reality is closer to a small refinery with magazine quality requirements bolted on top. You have a 200-280 degree Celsius solvent oven (the dryer), a chilled-water comfort space tighter than most pharmaceutical clean corridors (the pressroom), a hazardous-area solvent store with Ex-rated fittings, a dust collection problem at the finishing end measured in tonnes per shift, and a make-up air balance that has to satisfy AS 1668.2 across all of it. The duct work that ties this together is not generic HVAC. It is process ventilation, oven exhaust, hazardous-area extract and comfort HVAC running in parallel under one roof.

The Australian print industry is also in a particular moment. The newspaper print plants run by News Corp Australia and ACM are consolidating onto a smaller number of regional sites. Commercial print is dominated by IVE Group after Salmat absorption. Book publishing concentrates on Griffin Press in Adelaide, McPherson's at Maryborough, and Ligare in Sydney. Packaging is where most of the growth is — Visy, Orora, Pact, Detmold and a long list of contract converters. Every one of these operators is making capital decisions on plant upgrades, presses, dryers and the ventilation that supports them. The HVAC ductwork is rarely the headline line item, but it is one of the lines that decides whether the plant meets EPA conditions, passes WorkSafe inspections and runs without web breaks and register drift.

This guide is the engineering brief we use when our customers ask us to spec the duct manufacturing capacity for a print facility. It covers the process zones, the code stack, the print technologies that drive ventilation specs, the customer landscape in Australia, and how a duct shop should be tooled to fabricate for this sector reliably. It is not a substitute for a full mechanical design from a consulting engineer, but it sits beside that design as the practical fabrication-and-installation reference.

The print plant as a set of micro-environments

The most common mistake in print plant HVAC retrofits is treating the building as one volume. A modern print facility above 5,000 square metres is functionally five or six distinct micro-environments, each with its own temperature, humidity, pressure relationship and contamination profile. Ranked from most to least demanding on the mechanical services:

1. Dryer exhaust and oven stack — heatset dryers, IR / hot-air coating dryers, UV curing exhaust. 200-280 C typical, high VOC, condensable hydrocarbon mist, trace NOx. NFPA 86 territory with AS/NZS 60079 implications. Stainless steel duct, insulated, traced if external.
2. Pressroom comfort — 22-24 C at 50 percent RH for sheetfed, mid-volume digital and heatset commercial. F7 or F9 supply filtration. Slight positive pressure relative to dryer area and warehouse. Galvanised G90 spiral and rectangular.
3. Pre-press CTP — same 22-24 C / 50 percent RH band; tightest tolerance in the plant. Positive pressure to keep paper dust out.
4. Bindery and finishing — ambient HVAC plus a dedicated dust trunk at every cutter and folder. Galvanised duct, low-pressure baghouse or cartridge collector, 18-22 m/s transport velocity.
5. Ink and solvent store — classified hazardous area, Zone 1 or Zone 2 under AS/NZS 60079.10.1. Ex-rated exhaust fans, bonded earthed metal duct, no internal liners. Cool storage for certain ink chemistries.
6. Warehouse and paper store — ambient HVAC at controlled humidity to prevent curl, positive relative to outside. Make-up air typically flows from warehouse inward.
7. Office and customer-facing areas — standard commercial HVAC under AS 1668.2, separate packaged unit, not on the process loop.

Sharing trunks across these zones — pressroom return as dryer hood make-up, for instance — is how plants get solvent odours in the bindery, ink mist on the office AHU coils and a failed EPA monitoring report. Zone separation at duct level is non-negotiable. The fabrication shop has to deliver both galvanised and stainless duct in one project, with seam welding on the stainless side and locked or sealed seams on galvanised.

The code stack for print plant HVAC

Print plant HVAC sits at the intersection of three regulatory families: building ventilation, hazardous area electrical, and machinery safety. The Australian code stack we work to, in practice, is:

AS 1668.2 — Ventilation and Air Conditioning in Buildings

AS 1668.2 is the spine of the Australian mechanical ventilation framework — minimum outside air rates per occupant for office zones, and minimum exhaust rates for any space generating contaminants (which is every production zone in a print plant). It defines the supply / exhaust relationship that manages pressure differentials between zones and ties to AS 1668.1 on fire and smoke control of air-handling systems. Every print plant duct design in Australia starts with an AS 1668.2 compliance check. The practical implication for fabrication is duct leakage performance — class C or class D seam to EN 12237 and DW/144, which the Australian industry adopts by reference.

AS/NZS 60079 — Explosive Atmospheres

Where a print plant handles solvent inks, volume IPA fountain or gravure / solvent flexo chemistry, parts of the plant are explosive atmospheres. The parts relevant to duct work are AS/NZS 60079.10.1 (area classification — Zone 0 / Zone 1 / Zone 2), AS/NZS 60079.14 (electrical installation, driving the choice of Ex-rated motors, fans and instrumentation) and AS/NZS 60079.17 (inspection and maintenance). The duct itself is bonded steel — galvanised lower-risk, stainless higher-risk — earthed continuously, with no internal acoustic liners that hold static. PVC and fabric duct is excluded from any classified zone. Cleanout gaskets are conductive.

NFPA 33 — Spray Application

NFPA 33 is a US standard referenced by Australian insurers as best practice for spray-coating and solvent-coating operations inside a print plant — inline coaters, separate spray-coating booths, solvent-applied finishes on packaging substrates. It sets booth ventilation rates, duct construction, clean-out requirements and the interlock between the coater and the exhaust system. For fabrication: smooth-bore metal duct from booth to discharge, no horizontal collection runs, frequent clean-out doors, no flexible duct on the contaminated side.

NFPA 86 — Ovens and Furnaces

The heatset web offset dryer is, in NFPA 86 terms, an oven. It drives off solvent, holds the paper at temperature long enough to set the ink, and exhausts to an oxidiser. NFPA 86 sets the minimum exhaust rate (typically four air changes per minute of heated volume, with class A oven margins), the minimum dilution to keep the inlet below 25 percent of LEL, the burner shutdown interlock chain, and the duct construction between dryer hood and oxidiser inlet. In practice this is the most demanding duct in the plant: 304 stainless minimum, 316L preferred for chloride-bearing inks, TIG full-penetration longitudinal seams, expansion joints on any run over 10 metres, insulation rated for operating temperature plus margin, and external trace heating on roof runs to keep dewpoint above condensation.

AS 4024 — Safety of Machinery

AS 4024 covers the machinery safety side of any duct installation — guarding, isolation, lockout-tagout, access platforms. The duct contractor integrates access doors, ladders and platforms into the duct routing that meet AS 4024 reach and fall-protection requirements. Roof-mounted duct serving heatset dryers also needs anchor points, walkways and edge protection to AS/NZS 1657.

Print technologies and the ventilation each one drives

The print process technology decides the HVAC duct specification more than any other single factor. The five main processes in an Australian commercial environment are web offset (coldset and heatset), sheetfed offset, digital, gravure and flexographic.

Web offset — coldset

Coldset web offset is the newspaper process — continuous newsprint web, ink dries by absorption, no dryer, no oven exhaust requirement. The HVAC duct specification is dominated by paper-dust extraction at every web break, fluff capture at the folder, and pressroom comfort with humidity above 40 percent for static control. Pressrooms below that threshold see web breaks, register drift and operator shocks. Duct is galvanised G90 throughout — no solvent, no classified zone. Dust collection trunk at 18-22 m/s transport velocity, with clean-out doors at every elbow and a baghouse on the roof or in a dedicated outbuilding.

Web offset — heatset

Heatset web offset is the high-end commercial process for magazines, glossy inserts and catalogues on coated paper. The press runs the printed web through a dryer at 200-280 C with afterburner or RTO on the exhaust. Heatset ink chemistry uses high-boiling petroleum distillates as the carrier — the dryer evaporates the solvent and the RTO destroys it.

The duct specification is dominated by the dryer exhaust: 200-280 C, 1,500-3,000 ppm solvent vapour at full press speed, condensable ink mist and trace NOx from the dryer burner. The duct from the dryer hood to the RTO inlet has to be 304 or 316L stainless, fully welded seams, insulated, with expansion joints because the duct sees a 250 C swing every shift start. The pressroom holds 22-24 C and 50 percent RH on coated paper. Classified hazardous area covers the ink supply line and the immediate vicinity of the dryer hood — typically Zone 2 with a small Zone 1 envelope around bulk ink decanting. A typical heatset plant has 20-30 percent stainless duct on the dryer / RTO trunk and 70-80 percent galvanised on pressroom, bindery and warehouse.

Sheetfed offset

Sheetfed offset is the workhorse for high-quality commercial print, packaging cartons, books and labels in shorter runs. Ink dries by oxidation over hours, so there is no heatset-scale oven. Some lines run inline UV curing for spot varnish (adds UV exhaust and ozone removal) or an IR drying tower for inline coatings (small-scale dryer exhaust, NFPA 86 territory if above 200 C).

The duct specification is dominated by pressroom comfort and IPA fountain vapour management. Even alcohol-reduced fountains at 1-3 percent IPA produce significant cumulative evaporation across a pressroom of running presses. Duct is galvanised throughout except the IPA extract at the press, which is bonded earthed metal in line with AS/NZS 60079. Pressroom 22-24 C at 50 percent RH, F7 minimum supply filtration to keep dust off wet ink.

Digital print

Digital print covers HP Indigo, Canon, Xerox, Konica Minolta and Ricoh — toner or liquid-electrophotographic, low-VOC inks, low heat loads, ambient HVAC. The duct specification is essentially high-end commercial HVAC: galvanised throughout, F7 (F9 for colour-critical), constant temperature within plus or minus 1 C, no classified zone, no oven exhaust. In hybrid plants the digital room is positively pressured relative to the press hall to keep paper dust and solvent vapour out — the standard configuration at IVE Group and most regional printers with added digital capacity.

Gravure

Gravure is a high-volume process — engraved cylinder, solvent-based ink, very high VOC loading. In Australia it is concentrated in flexible packaging and decor rather than publication. Every gravure deck has its own enclosed solvent dryer feeding a solvent recovery unit (carbon adsorption with steam regen) or RTO. The whole press hall is a classified hazardous area under AS/NZS 60079 — Zone 1 close to the cylinders, Zone 2 across the rest. Duct is fully welded stainless throughout the contaminated side, with bonded earthing, conductive gaskets and Ex-rated fans and dampers. The installation is closer to a chemical plant than a print plant.

Flexographic

Flexographic printing dominates corrugated packaging, labels and flexible film. Modern flexo runs water-based ink (corrugated brown box), solvent-based ink (non-absorbent film) or UV-cured ink (labels and high-end packaging):

• Water-based flexo — minimal ventilation beyond comfort HVAC. Galvanised duct throughout, no classified zone, no oxidiser required.
• Solvent-based flexo — equivalent specification to gravure on the contaminated side. Fully welded stainless duct from dryer to RTO, AS/NZS 60079 Zone 2 across the press hall.
• UV flexo — UV curing tower on each deck with localised ozone exhaust. Galvanised duct, no classified zone.

Corrugated post-print plants (Visy, Orora and the independent box plants) are almost entirely water-based flexo and have the simplest duct specs in the sector. Flexible packaging on solvent flexo has the most demanding.

The dryer exhaust train and the RTO

For any heatset web offset, gravure or solvent flexo plant, the single most consequential piece of duct work in the building is the train from the dryer hood to the regenerative thermal oxidiser to the stack. The duct in that train carries the entire emissions liability of the plant, the entire heat-recovery opportunity, and the entire risk if any joint fails. It is worth treating in its own section.

A regenerative thermal oxidiser (RTO) is a piece of pollution control equipment that destroys VOCs by raising the exhaust gas stream to combustion temperature (800-850 C) through a chamber packed with ceramic media. The media absorbs heat from the hot gas leaving the chamber and gives it back to the next charge of cooler gas entering the chamber. After two or three charges the system is largely self-heating and the supplementary burner runs at minimum. Destruction efficiency on common print solvents is routinely 98-99 percent. Without an RTO (or an equivalent solvent recovery unit) a heatset or gravure plant cannot run legally under any Australian state EPA framework.

The duct train into the RTO carries the dryer exhaust at 200-280 C and a VOC concentration that varies with press speed. The duct material is 304 stainless minimum, 316L preferred for chloride-bearing inks, fully welded longitudinal seam with TIG and full penetration. Wall thickness is 1.5-2 mm depending on diameter and span. Insulation is rated for the operating temperature plus a margin and clad in galvanised sheet metal. Trace heating is mandatory on any external roof run because dropping the gas below the dewpoint condenses the heaviest hydrocarbons onto the duct wall and clogs the RTO inlet over time.

The duct train out of the RTO carries cleaned hot gas, usually 150-200 C after heat recovery. The duct material can step down to 304 stainless or even galvanised steel for the cooler stretches, depending on the heat-recovery configuration. The stack height is set by AS 3580 and local EPA dispersion modelling.

The recovered heat off an RTO is one of the largest energy opportunities in any print plant. Typical recovery configurations are:

• Direct hot-air recovery to dryer combustion air — preheats the burner inlet, drops dryer gas consumption by 15-25 percent.
• Indirect water-glycol recovery to make-up air heating — heat-exchanger on the RTO outlet, glycol loop to AHU pre-heat coils. Cuts winter gas consumption substantially.
• Indirect water-glycol recovery to ink heating, shop hot water, plate processor — uses lower-grade heat for ancillary loads.

The recovery duct work is mostly galvanised steel on the cool side and stainless on the hot side. The duct contractor has to be able to fabricate both materials to a quality consistent with the rest of the build — which is a meaningful constraint on which fabrication shops can credibly tender for a heatset job.

Pressroom comfort and humidity control

The pressroom on any quality-critical print line is a controlled environment. Temperature and humidity affect ink viscosity, paper dimensional stability, register accuracy, static behaviour on dry substrates and the consistency of any colour-critical work. The industry target for sheetfed, mid-volume digital and high-end commercial heatset is 22-24 C dry bulb at 50 percent relative humidity. Tolerance is typically plus or minus 2 C and plus or minus 5 percent RH; tighter on fine-art reproduction, security printing and high-end packaging.

Holding 22-24 C and 50 percent RH year-round in an Australian climate is a significant mechanical task. Melbourne and Sydney summers run 35-40 C and below 30 percent RH at peak; Brisbane and Perth summers run higher. Winters can drop below 5 C at night, with RH bouncing between 30 and 95 percent depending on weather. The pressroom AHU has to dehumidify in summer (chilled-water coil with reheat to control coil leaving conditions) and humidify in winter (steam or evaporative humidifier downstream of the heating coil).

The duct system for pressroom comfort is, mechanically, conventional commercial HVAC. Galvanised G90 spiral duct on the supply side because spiral has lower leakage and better acoustic performance than seamed rectangular at the same area. Rectangular duct where space is constrained or where the run is short. F7 or F9 filtration at the AHU, with optional carbon stage if the plant is downwind of a recycling depot or other odour source. Return air via a low-velocity ceiling plenum or via dedicated return duct — the choice depends on plant ceiling height and acoustic preferences.

Acoustic performance matters in a modern pressroom because the press itself runs at 75-85 dB(A) at the operator position and any additional 5 dB from the HVAC noise pushes the cumulative exposure into the WorkSafe action zone. Industry practice is to design the supply diffusers for NC-50 maximum at occupancy, with internally lined supply duct only in the immediate run from the AHU. Internal acoustic liner is excluded from any duct serving a classified zone (AS/NZS 60079) and from any duct that has to be cleanable to AS/NZS 3666 for legionella control.

Pre-press CTP plate making

The pre-press computer-to-plate (CTP) room is a smaller volume than the pressroom but it holds the tightest tolerance band in the plant. CTP plates are aluminium sheet with a photopolymer or thermal emulsion coating; they are imaged in a CTP imager, processed in a developer line and supplied to the press. Plate dimensional stability and emulsion thickness are both temperature-sensitive, so the CTP room holds 22-24 C at 50 percent RH within plus or minus 1 C and plus or minus 5 percent RH.

The room is positively pressured relative to the pressroom and the warehouse to keep paper dust and solvent vapour out. Filtration on the supply is F9 minimum. Duct material is galvanised G90 throughout. The volume is small — typically 200-500 m² of floor area in a mid-sized plant — so the duct sizes are small and the AHU is a packaged unit dedicated to this room. The mechanical engineer treats the CTP room more like a laboratory than a production zone.

Bindery, finishing and the paper-dust problem

The bindery and finishing end of a print plant is where the printed substrate becomes the finished product — folded sections, gathered books, perfect-bound or saddle-stitched magazines, die-cut cartons, trimmed labels. Every one of these processes generates paper dust. A high-speed perfect-binding line running at 12,000 books per hour generates a continuous stream of fine paper dust from the spine grinder, the trim knives and the gathering chain.

The dust load is significant. A mid-sized commercial bindery generates 20-50 kilograms of paper dust per shift across all the lines. That dust has to be captured at source because it migrates rapidly into the rest of the plant — and once it gets into the pressroom it lands on wet ink and ruins the printed sheet.

The HVAC duct specification for the bindery is two parallel systems: a comfort HVAC providing tempered air for the operators, and a dedicated low-pressure dust extraction trunk taking paper dust from every cutter, folder, gatherer and trimmer back to a baghouse or cartridge collector. The dust trunk is galvanised G90 with smooth interior seams to prevent fibre accumulation, transport velocity 18-22 m/s, clean-out doors at every elbow, and bonded and earthed continuously. Static control matters because dry paper dust at low humidity is a recognised dust-explosion hazard — it is classified as Class II Group G in legacy US practice and treated equivalently under Australian dust-explosion guidance.

The baghouse or cartridge collector is sized for the cumulative dust load with a safety margin of 30-50 percent on the design flow. Discharge is either back into the plant after filtration (cleaner air recirculation) or to atmosphere depending on local odour and dust rules. The recovered paper dust is bagged and sold to recycling or to firestarter manufacturers — it is a small revenue stream rather than a waste cost.

Mail house, lettershop and warehouse zones

The mail house or lettershop is the inserting, addressing and despatch end of a magazine or catalogue plant. It is essentially a logistics environment with light machinery. The HVAC is comfort-grade ambient, AS 1668.2 minimum outside air rates for the occupancy, F5 or F7 filtration, no special humidity control. Duct is galvanised G90 throughout. Dust extraction is local at any high-speed inserter that generates trim waste, but the dust load is far lower than in the bindery proper.

The warehouse and paper store at the back end of every print plant is the largest single volume in the building and the simplest from a duct point of view. It holds finished product going out and inbound paper rolls or skids coming in. The HVAC target is 18-22 C with humidity above 45 percent to control paper curl on the inbound side. The duct system is large-diameter galvanised, low velocity, large supply diffusers, gravity or wall-fan return. Make-up air for the rest of the plant typically flows from the warehouse zone inward, so the warehouse is the positive-pressure source for the whole site.

Some ink chemistries — particularly UV inks and certain digital ink formulations — require cool storage below 20 C with humidity below 60 percent. The ink store is therefore a separate smaller room within the warehouse with its own packaged AHU or split system. Where solvent inks are stored in volume, the ink store is also a classified hazardous area under AS/NZS 60079 with Ex-rated lighting and exhaust.

The Australian print sector — who runs these plants

The Australian print sector is concentrated. Most of the duct work spend in a given year goes to a small set of operators, with a long tail of regional and trade printers below them.

Newspaper print

News Corp Australia runs the largest newspaper print footprint in the country, printing The Australian, the Daily Telegraph (NSW), Herald Sun (VIC), Courier Mail (QLD), Adelaide Advertiser (SA), Mercury (TAS) and NT News. The print network is a small number of large heatset and coldset combination plants: Chullora NSW (Sydney), Westgate Park VIC (Melbourne), Murarrie QLD (Brisbane), Mile End SA (Adelaide) and Canning Vale WA (Perth). These are the largest and most demanding print HVAC environments in Australia — each combines coldset for daily mastheads with heatset for inserts and magazine work, plus full bindery and mail-house operations, mixing stainless dryer trunk, galvanised pressroom and bindery, and large-volume warehouse make-up.

Nine Publishing (formerly Fairfax) prints the Sydney Morning Herald, The Age and the Australian Financial Review. Since Nine's acquisition of Fairfax in 2018, print operations have largely been contracted out to News Corp and other commercial printers; the legacy Fairfax print sites at Chullora and Tullamarine have been wound down or sold.

Australian Community Media (ACM) runs the largest regional newspaper print footprint — Canberra Times, Newcastle Herald, Examiner (Tas), Border Mail and approximately 140 regional and community mastheads. ACM sites are smaller, mostly coldset only, with simpler bindery — dominated by coldset pressroom comfort, paper-dust extraction and warehouse make-up, no heatset dryer trunk required. Country Press Australia represents the long tail of independent regional newspaper printers — small single-tower coldset plants making up a significant share of total newspaper volume by site count.

Commercial print

IVE Group (ASX:IGL) is the largest commercial printer in Australia after the Salmat acquisition, running heatset web offset, sheetfed offset, digital, bindery, mail house and distribution across NSW, Victoria, Queensland and South Australia. The IVE plants are the largest commercial print HVAC environments outside the News Corp newspaper sites.

Ovato Limited (formerly PMP Limited) was the second-largest commercial printer until its collapse in 2020. Ovato print assets were sold piecemeal — some to IVE, some to smaller operators. Legacy PMP Print brand survives in some Salmat-era divestments at a smaller scale. Bauer Media (acquired by Mercury Capital and rebranded Are Media) publishes Australian Women's Weekly, Woman's Day, Better Homes and Gardens and most Australian women's magazine titles, contracting print to IVE and others. News Magazines publishes TV Week and the News Corp lifestyle supplements through News Corp's commercial print division.

Book publishing and book print

Griffin Press in Adelaide (ICP Group) is the largest dedicated book printer in Australia — sheetfed offset, web offset and digital for trade publishing, education and case-bound work. McPherson's Printing Group at Maryborough VIC has been in continuous operation since the 1960s, running web offset and sheetfed for trade and educational titles. Ligare in Sydney rounds out major book capacity with sheetfed offset and digital for short-run and academic publishing. HarperCollins Distribution and Pearson Australia are the two largest book publishers operating their own significant warehouse and distribution sites without internal print — both contract to Griffin, McPherson's, Ligare or offshore.

Packaging print

Packaging is where most of the growth in Australian print is concentrated. Visy is the largest privately held packaging company in Australia with approximately 30 corrugated and folding-carton sites — corrugated post-print on water-based flexo, folding-carton on sheetfed offset, plus substantial inline coating. Orora Limited (ASX:ORA) is the second major operator, running cardboard, folding-carton, glass and aluminium beverage packaging from multiple sites. Pact Group (ASX:PGH) operates plastic, food and paper packaging across Australia — the print-relevant lines are folding-carton and paper-bag printing on sheetfed and water-flexo.

Detmold Group in Adelaide is the largest paperboard cup and food-service packaging manufacturer in the country, running flexo and offset for cup wraps, board converting and folding cartons. Detpak is the Detmold food-service division with its own dedicated print and converting sites. Multi-Color Corporation, Hally Labels and Avery Dennison are the major label and flexible packaging operators — a mix of solvent flexo, water flexo, UV flexo and digital, including classified hazardous-area duct on the solvent flexo lines.

Duct material selection — galvanised, stainless and the trade-offs

The duct material selection in a print plant is a binary decision per zone: galvanised for general comfort HVAC, dust extraction and lower-temperature exhaust; stainless for dryer / oven exhaust and any classified zone where solvent contact is direct. Getting the boundary right is the single largest cost lever on the duct work package.

Galvanised steel is the default print plant duct material. G90 coating (270 g/m² zinc) is industry standard for indoor work; G115 (345 g/m²) for any outdoor or roof-mounted run. Galvanised is suitable for:

• All pressroom comfort HVAC supply and return.
• Pre-press CTP supply, return and exhaust.
• Bindery and finishing comfort HVAC and the dust extraction trunk.
• Warehouse make-up air, supply and return.
• Mail house and office HVAC.
• Coldset newspaper press hall and dust extraction.
• Water-based flexo (corrugated post-print) supply, return and exhaust.
• Cool-side duct downstream of any RTO heat recovery once the gas is below 150 C.

Galvanised duct in a typical heatset commercial plant is 70-80 percent of total duct linear metres and roughly 60-70 percent of total duct cost.

Stainless steel (304 or 316L) is the required material for:

• Heatset web offset dryer hood to RTO inlet — hot, solvent-laden, condensable.
• Sheetfed UV exhaust if the UV tower runs above 200 C surface temperature.
• Sheetfed IR dryer exhaust on inline coating lines.
• Gravure dryer to solvent recovery or RTO.
• Solvent flexo dryer to solvent recovery or RTO.
• Ink and solvent store extract where the chemistry is corrosive or where condensation is expected.
• Spray-booth exhaust under NFPA 33.
• Any duct serving an oven exhaust under NFPA 86.

304 stainless is acceptable for most heatset and gravure exhaust trains. 316L is preferred where the ink chemistry includes chloride compounds — some newspaper inks, some packaging-grade solvent inks — because chloride attack on 304 can cause stress corrosion cracking on the welded longitudinal seam over a 15-year service life. The cost differential between 304 and 316L is roughly 25-40 percent at sheet level, so the choice matters on a large plant.

Seam construction on stainless dryer duct is TIG-welded full-penetration longitudinal seam with the root side cleaned and passivated. Snap-lock or Pittsburgh seam is unacceptable on this duty — the seam has to hold at temperature and at slight positive or negative pressure relative to surrounding building. The seam welder on the duct fabrication shop floor has to be capable of producing TIG seams on sheet stainless at a rate that supports the project schedule, which constrains the fabrication shop selection.

Hazardous area duct work and Ex-rated fittings

Where a print plant operates with solvent inks — heatset, gravure, solvent flexo, certain ink stores — the duct work in the affected zones is part of an installation that has to comply with AS/NZS 60079.10.1 (area classification) and AS/NZS 60079.14 (electrical installation). The duct itself is generally bonded metal earthed continuously to a common earth bar, but the fans, dampers, sensors, lighting and control gear in the classified zone all have to be Ex-rated.

The practical consequences for the duct contractor are:

• Earthing — every duct section is bonded across joints with a continuity strap, and the entire system is earthed to a single ground point per zone. Plastic flange gaskets are excluded; conductive gaskets specified.
• Ex-rated fans — exhaust fans in classified zones are Ex e or Ex d motors with corresponding terminal boxes. The fan housing is metal not fibreglass. Bearing temperature monitoring is mandatory on the larger fans.
• Ex-rated dampers — actuators on dampers in classified zones are Ex-rated electric or pneumatic. Spring-return pneumatic actuators are common because they fail safe to a known position on air loss.
• Sensor selection — temperature sensors, pressure sensors and flow sensors in classified zones are Ex-rated, with intrinsically safe wiring back to a barrier panel in the safe area.
• Cleanouts — clean-out doors on solvent duct are sealed with conductive gaskets and bonded across the seal. No internal liners.
• Fire-rated penetrations — duct passing through a fire-rated wall between classified and non-classified zones uses an approved fire-stop sleeve that maintains both the fire rating and the bonding continuity.

The duct fabrication shop does not have to be Ex-certified to fabricate duct for a classified zone, but the installation contractor does have to understand the discipline — and the duct fabrication has to support it through correct bonding tabs, no internal acoustic liners and the right gasket selection.

Acoustic targets — NC-50 and the practical implications

Print plants are noisy. A running heatset web offset press generates 90-95 dB(A) at the operator position; a running sheetfed press generates 80-85 dB(A); a bindery line with high-speed folder and trimmer running generates 85-90 dB(A). The HVAC duct system has to fit into that acoustic environment without adding measurable noise at the operator station.

The industry target is NC-50 maximum at the operator position from the HVAC alone. NC-50 corresponds roughly to 55-58 dB(A) at the diffuser. Achieving this means:

• Supply diffusers sized for 5-6 m/s face velocity maximum, not the 8-10 m/s typical of commercial offices.
• Trunk velocity 8-12 m/s on supply, lower on return.
• Internally lined supply duct only in the immediate run from the AHU (10-15 m maximum) because acoustic liner is excluded from classified zones and from any duct that has to be cleanable.
• Inline silencers in the supply trunk where the run is too short for natural attenuation.
• Vibration isolation on fan mounts and flexible connections at every AHU and exhaust fan.

Acoustic performance is rarely the binding constraint on a print plant duct design — the dryer exhaust spec, the hazardous-area spec and the dust extraction spec all dominate. But it does set the supply diffuser sizing and therefore the supply trunk sizing, and it does drive the choice between spiral and rectangular duct on the comfort HVAC side. Spiral duct is acoustically better than rectangular at the same area because it does not flex and radiate noise the way a sheet metal panel does.

Make-up air and pressure balance across zones

A print plant has multiple exhaust streams running simultaneously: dryer exhaust, dust extraction, ink store extract, pressroom return going to the AHU, bindery exhaust. Each one removes air from the building. That air has to be replaced — and the replacement has to be at a rate that maintains the design pressure differential between zones.

The design pressure relationships in a typical heatset commercial plant are:

• Office / customer-facing — neutral or slight positive relative to outside (10-15 Pa).
• Pre-press CTP — positive relative to pressroom (5-10 Pa) and to office (5-10 Pa).
• Pressroom — positive relative to dryer hood area, warehouse and bindery (5-10 Pa).
• Bindery — neutral or slight negative relative to pressroom, positive relative to outside.
• Dryer hood / oven area — slight negative relative to pressroom (5 Pa) to keep solvent vapour out of the pressroom.
• Ink and solvent store — strong negative relative to everything else (15-25 Pa) to contain solvent vapour.
• Warehouse — slight positive relative to outside, neutral or slight negative relative to pressroom.

Holding these differentials in operation requires a make-up air system that responds to the exhaust load. Typical configurations are dedicated make-up air handlers (MUAHs) for the larger zones, with VFD-driven supply fans modulating on a pressure-differential signal across each zone boundary. The duct system has to be sized for the design flow plus a margin, with balancing dampers at every branch.

Make-up air is also the largest single heating and cooling load in the plant during the extreme weeks of the year. In a Melbourne winter the make-up air heating load can exceed 1 MW for a large heatset plant — which is why the heat recovery off the RTO is such a valuable energy stream. Tying RTO heat recovery into make-up air pre-heat is one of the few investments that pays back in 3-5 years on its own, before any consideration of emissions compliance.

Fire and smoke control across zones

A print plant has multiple fire-load zones — paper warehouse, ink and solvent store, dryer / oven, pressroom, finishing. The duct system has to provide fire and smoke separation between zones in line with AS 1668.1 and the National Construction Code Section J. Duct passing through a fire-rated wall has fire dampers (or smoke dampers, depending on the rating) installed at the wall line, certified to AS 1682 and held open by a fusible link or smoke detector. The dampers fail closed on fire and isolate the duct system.

The practical considerations for the duct contractor are:

• Fire dampers add length and weight at every wall penetration — they need access doors immediately on the non-classified side for maintenance.
• Duct passing through the dryer / oven exhaust train through a wall needs a high-temperature damper (rated for 250 C minimum, often 400 C) which is a specialty item.
• The HVAC controls have to integrate with the fire alarm — typically a fire trip closes all dampers and shuts down all fans except dedicated smoke exhaust fans.
• Solvent ink and solvent store ventilation has its own interlocks — loss of exhaust ventilation triggers an ink supply isolation valve to close.

Insulation, lagging and external duct

Two distinct insulation requirements operate in a print plant. The first is thermal insulation on cool ducts (chilled water supply, conditioned air supply) to prevent condensation and to limit energy loss. The second is high-temperature insulation on hot ducts (dryer exhaust, RTO inlet, RTO outlet) to keep the gas above its dewpoint and to protect personnel from burns.

For cool ducts the standard is 50 mm of mineral wool with foil vapour barrier on the outside, taped and sealed at joints. For chilled-water ducts in humid spaces (bindery, warehouse, parts of the pressroom in summer) 75 mm is recommended. For external supply duct on a roof run, 100 mm of weatherproof insulation clad in galvanised sheet is standard.

For hot ducts the insulation is calcium silicate or ceramic-fibre blanket, 75-100 mm thick depending on operating temperature, clad in galvanised or stainless sheet metal. The cladding is the visible finish and has to seal against weather on external runs. Trace heating is installed under the insulation on any external run where the gas could drop below the dewpoint in winter — typically 30-40 W/m of self-regulating cable controlled by an ambient thermostat. The trace heating is mandatory on heatset dryer trunk in Melbourne and any colder climate; less critical in Brisbane and Perth.

How an SBKJ duct machine line supports a print-sector duct contractor

A duct contractor tendering for print-sector work needs a fabrication line that can switch between materials, gauges and seam types within a single shift. A typical large commercial print HVAC project mix is 70-80 percent galvanised G90 spiral and rectangular duct, 10-20 percent stainless 304 or 316L for dryer exhaust and classified zones, and a small fraction of high-temperature alloy duct for the hottest oven runs.

The SBKJ machine configuration we typically recommend for a contractor serving this sector is:

• SBAL-V Auto Duct Line in the galvanised + stainless option — handles 0.6-1.5 mm thickness, 1,000-1,300 mm coil width, with both galvanised and stainless coil change-over without changing the tooling. Output 16-22 m/min of rectangular TDF duct on galvanised; 12-15 m/min on stainless. Single-shift capacity covers the comfort HVAC and bindery duct demand on a major project.
• SBTF-1602 Spiral Tubeformer — for round spiral duct in galvanised. Used for the pressroom supply and the bindery exhaust where round duct is acoustically and aerodynamically preferred over rectangular. Diameter range 100-1,600 mm.
• TIG seam welder for stainless dryer-exhaust duct fabrication. Full-penetration longitudinal seam on 1.5-2 mm 304 or 316L sheet, with root protection and post-weld passivation. Necessary for any dryer trunk or RTO inlet fabrication.

This three-machine combination covers the full duct work scope on a print-sector project from a single fabrication floor. The contractor avoids subcontracting the stainless work to a specialty shop (which adds 30-50 percent cost on stainless line items and lengthens the project schedule) and avoids the alternative of running a single dual-purpose line at lower productivity for galvanised work.

Lead time, sequencing and project-stage duct delivery

A print plant duct project typically runs in three stages over 8-14 months from contract to commissioning:

• Stage 1 — foundation and superstructure (months 1-4). Duct routing is fixed at this stage but no duct is on site yet. The fabrication shop is sizing materials and ordering coil. The dryer exhaust stainless coil order is the long-lead item — 12-16 weeks for 316L sheet to landed in Australian port.
• Stage 2 — duct installation (months 4-10). The duct goes in zone by zone, usually starting with warehouse and office HVAC (because the ceiling is up first), then bindery and pre-press, then pressroom, then dryer / RTO. The stainless dryer trunk is the last duct in because it ties to the press and oven which are commissioned late in the schedule.
• Stage 3 — commissioning and balancing (months 10-14). Air balancing across zones, pressure differential testing, smoke testing for fire dampers, witness testing of dryer exhaust with the RTO running. EPA compliance test on the stack. Final acceptance.

The duct contractor's exposure is concentrated in stages 2 and 3. A delay in stainless dryer trunk delivery delays the whole press commissioning — and on a heatset newspaper or commercial site, every week of delay on press commissioning is a six-figure revenue loss to the operator. The fabrication shop that can hold the stainless schedule is the one that wins the next project.

Energy, sustainability and the RTO heat-recovery business case

The print sector has been under continuous energy and emissions pressure for two decades. Heatset is the most exposed because the dryer is the largest single energy load in the plant and the most directly tied to emissions. Coldset and sheetfed are less exposed but still under cost pressure from rising electricity and gas prices.

The single largest energy improvement available on a heatset line is RTO heat recovery into the make-up air and the dryer combustion air. Typical savings on a mid-sized heatset commercial plant are:

• 15-25 percent reduction in dryer gas consumption from preheating dryer combustion air with recovered RTO heat.
• 30-50 percent reduction in winter make-up air heating gas consumption from recovering RTO heat into the make-up air pre-heat coils.
• 5-10 percent reduction in shop hot water and ink heating from lower-grade heat off the same RTO loop.

The duct work to support these recovery loops is mostly galvanised steel on the cool side and stainless on the hot side, with a heat exchanger between them. The capital cost of the recovery duct work is 10-15 percent of the total HVAC duct package on a heatset plant, and the payback on the gas saving alone is 3-5 years at current Australian gas prices. With the carbon-emissions reporting and EPA framework continuing to tighten, the case strengthens every year.

For coldset newspaper and sheetfed commercial plants without a dryer, the heat-recovery opportunity is smaller — typically a sensible-heat exchanger on the pressroom return into the make-up air pre-heat, recovering 30-40 percent of the building heating energy. Payback on this is longer (6-8 years) but the duct work to support it is straightforward galvanised.

Common failure modes — what we see in the field

We commission print plant duct projects regularly, and the failure modes tend to repeat. The five most common are:

1. Galvanised duct on the dryer exhaust trunk. Someone has value-engineered the stainless out of the heatset trunk. The duct survives commissioning, runs for 18 months, and then the seams start failing where solvent condensation has stripped the zinc. Repair requires shutting the press down for a week and replacing the trunk with stainless after the fact.
2. Shared duct between dryer exhaust and pressroom return. A short-cut on the design has tied the pressroom return into the dryer exhaust trunk to save a separate fan. Result is solvent vapour back into the pressroom on any pressure swing, and the AHU coils contaminated within months.
3. No expansion joints on the dryer trunk. A 30 metre dryer trunk that sees a 250 C swing every shift expands and contracts by 80-100 mm cumulatively. Without expansion joints the duct cracks at the first elbow.
4. Inadequate dust extraction at the folder. The bindery dust trunk is undersized and the transport velocity drops below 15 m/s. Paper dust settles in the duct, eventually blocks it, and the static buildup on the residual flow becomes a fire risk.
5. Wrong filtration on the pressroom supply. The supply air filtration is M5 or F5 (typical commercial spec) rather than F7 or F9 (industry standard for printing). The result is airborne dust on wet ink and rejected sheets — the cost of the rejected work in a single month often exceeds the cost of upgrading the filtration for the life of the AHU.

All five are preventable at design stage. The cost of catching them at design is one or two engineer-days of review. The cost of catching them at commissioning is rework. The cost of catching them six months into operation is a production shutdown.

What we deliver to print-sector duct contractors

SBKJ supplies the fabrication machinery — auto duct lines, spiral tubeformers, seam welders, plasma cutters and the supporting tooling — that lets a duct contractor or fabrication shop build print-plant duct work to the specs in this guide. We do not sell the duct itself; we sell the machines that make it.

Our standard print-sector configuration is the SBAL-V auto duct line in the galvanised + stainless option, the SBTF-1602 spiral tubeformer, and the TIG seam welder for stainless dryer-exhaust fabrication. The three machines together cover the full duct scope on a major print HVAC project from a single fabrication floor. The combination is in service with print-sector duct contractors and large in-house fabrication shops on five continents.

If you are quoting a print-sector HVAC duct package — heatset web offset, sheetfed commercial, book print, packaging or any of the other zones described above — we are happy to walk through the duct scope with one of our engineers and recommend the right machine specification for your shop. Our engineers reply within 12 hours and the discussion is always with a mechanical engineer rather than a salesperson.

Discuss your print-sector duct fabrication setup with an SBKJ engineer →

FAQ

Why does a print plant need different HVAC zoning to a general factory?

A print plant is really four or five micro-environments under one roof — dryer exhaust at 200-280 C, hazardous-area solvent zones, pressroom comfort at 22-24 C / 50 percent RH, bindery dust extraction, and ambient warehouse. Putting any two on a shared trunk causes contamination, register drift and compliance failures.

Which Australian standards apply to print plant ductwork?

AS 1668.2 for mechanical ventilation, AS/NZS 60079 for hazardous areas where solvent inks are in use, AS 4024 for machinery safety around the duct runs, AS/NZS 1657 for roof access platforms, and AS 1682 for fire and smoke dampers. NFPA 33 (spray application) and NFPA 86 (industrial ovens) are referenced as best practice by Australian insurers for any solvent-coating or heatset dryer operation.

Can galvanised duct handle a heatset web offset dryer exhaust?

Not directly. The dryer stream is 200-280 C with solvent vapour and condensable mist — that combination strips zinc from galvanised duct within 12-24 months. Specify 304 or 316L stainless, fully welded longitudinal seams, insulated and trace-heated. Galvanised is fine for 70-80 percent of the rest of the building.

What does a regenerative thermal oxidiser do for a print plant?

An RTO destroys VOCs in dryer exhaust at 800-850 C through ceramic media beds with regenerative heat exchange. Destruction efficiency above 98 percent on common print solvents. It is both the emissions compliance device and the primary heat-recovery source — recovered heat preheats dryer combustion air and make-up air, cutting gas consumption by 15-50 percent depending on configuration.

What HVAC temperature and humidity should a pressroom hold?

22-24 C dry bulb at 50 percent relative humidity for sheetfed offset, mid-volume digital and heatset commercial. Tolerance plus or minus 2 C and plus or minus 5 percent RH. Coldset newspaper presses are more forgiving and run at ambient with humidity above 40 percent for static control. CTP plate rooms hold the same tight 22-24 C / 50 percent RH band as the pressroom.

How is paper dust handled in finishing and bindery?

A dedicated low-pressure dust trunk at every cutter, folder, gatherer and trimmer, sized at 18-22 m/s transport velocity, in galvanised G90 duct with clean-out doors at every elbow, tied back to a baghouse or cartridge collector. The system is bonded and earthed throughout because dry paper dust at low humidity is a recognised dust-explosion hazard.