Ductwork & Air Distribution

Ductwork carries air between air handling units, fans and the spaces they serve: supply, return, outside air and exhaust. Air distribution includes the grilles, registers and diffusers at each end, the balancing dampers that set airflows, the flexible connections to terminal units, the insulation and vapour barrier on chilled ducts, internal acoustic lining, and the fire and smoke dampers where ducts pass through fire-rated walls and floors.

Fire and smoke dampers close when heat or a fire alarm signal is detected, to stop fire and smoke travelling through the ductwork. They are life-safety devices with their own inspection and testing regimes, and they are commonly found missing, painted shut, obstructed or never connected to the fire alarm.

What shortens life:

• Torn vapour barriers on chilled ductwork.
• Corrosive and greasy exhausts.
• Fit-outs that cut, reroute and kink ductwork without rebalancing.
• Poor filtration upstream, which loads ducts with dust.
• Rodents and pests in older systems.

Air leakage

Joints and seams leak as sealants age, wasting fan energy and delivering less air than designed. Leaky return ductwork in ceilings draws in dust and fibres.

Condensation on chilled ductwork

Supply ducts carrying cold air sweat if their insulation or vapour barrier is torn, compressed or missing. Water wets the insulation, drips onto ceilings, and corrodes the duct and its supports.

Dirt accumulation and hygiene

Dust, debris and construction residue accumulate inside ducts, particularly where filtration has been poor. In humid conditions, microbes grow on the dirt. Internal acoustic lining erodes and sheds fibres into the airstream.

Flexible duct problems

Long, sagging, kinked or crushed flexible duct restricts airflow; it tears and leaks; in roof spaces it degrades with heat.

Loss of balance

Fit-outs add, remove and relocate diffusers and adjust dampers without rebalancing. Some areas get too much air, others too little, and the system no longer matches its design.

Fire and smoke damper failure

Dampers corrode, seize, are obstructed by cables or debris, are painted or taped shut, or were never installed or connected. A damper that does not close lets fire and smoke through a fire-rated wall or floor.

Hazardous materials

Older ductwork can contain asbestos in flexible connectors, gaskets, duct lagging and some insulation.

Noise and draughts

High air velocities, throttled dampers near outlets and poorly selected diffusers generate noise and dump cold air onto occupants. Fit-outs that move partitions without moving diffusers create draughty and stuffy spots.

Corrosion in wet and chemical exhausts

Exhausts from pools, laundries, kitchens and laboratories carry moisture and chemicals that corrode galvanised ductwork from the inside; corrosion shows first at the lowest points and joints where condensate collects.

In ceiling voids and risers

• Torn or missing insulation; wet insulation; condensation drips; rust on ducts and hangers.
• Flexible ducts sagging, kinked, crushed or disconnected.
• Dust and debris visible inside open ducts and at grilles.
• Fire dampers: access panels, fusible links, obstruction, painted blades.
• Older materials: flexible connectors and lagging of the asbestos era.

In occupied spaces

• Dust streaks around supply diffusers.
• Draughts, noise, whistling.
• Hot and cold spots after fit-outs.
• Water stains from condensation on ceilings.

In the records

• Test and balance reports.
• Duct cleaning and hygiene inspection reports.
• Fire damper inspection and test records.
• Fit-out records.
• Asbestos register.

Findings are graded by what they demand: safety (can hurt someone now), failure (failed and damaging the building), condition (distress present and progressing), lifecycle (renewal due on age and exposure), deadline (a regulator or ordinance sets the date), check (investigate before sizing works) and nil (cosmetic or stable).

A mechanical services engineer leads, with a ventilation hygiene specialist and a fire damper inspector.

• Visual inspection of a representative sample of ductwork, insulation, vapour barrier, flexible connections and supports, prioritising risers, plant rooms and areas with complaints.
• Hygiene inspection by camera and access panels, with dust samples, to AS/NZS 3666, BESA TR/19 or NADCA ACR practice, to decide whether cleaning is needed.
• Airflow measurement at a sample of diffusers and grilles against design, and a review of the latest test and balance report.
• Fire and smoke damper survey: location against every fire-rated wall and floor the ductwork passes, access panel present, blade and spring condition, fusible link, release and drop test, connection to the fire alarm where required.
• Leakage testing of sections to DW/143 or SMACNA methods where energy use or airflow shortfalls warrant.
• Asbestos sampling of flexible connectors, gaskets, lagging and older insulation.
• Noise survey where complaints exist.

The report should give a fire damper register with location, type, access and test result for every damper; hygiene condition; airflow and balance findings; insulation condition; hazardous materials; and prioritised works.

• Fire and smoke dampers: install missing dampers, replace failed or corroded units, remove obstructions and paint, fit access panels, connect motorised dampers to the alarm, and test and register every damper.
• Cleaning by brushing, air washing and vacuum to the hygiene standard; cleaning is pointless without fixing the filtration or moisture problem that dirtied the ducts.
• Lining replacement: replace eroding internal lining with faced or perforated-metal-faced lining, or move attenuation to dedicated attenuators.
• Insulation and vapour barrier repair on chilled ductwork, sealing every joint.
• Flexible duct replacement: short, straight, supported runs.
• Sealing: reseal joints; aerosol internal sealing for inaccessible sections.
• Rebalancing after fit-outs, with diffusers relocated to suit partitions.
• Corrosion: replace corroded wet-exhaust sections in stainless steel with drainage at low points.
• Asbestos removal by licensed contractors.

Inspection and testing are lump sums with rates per damper tested. Fire damper rectification is priced per damper, with access panels and ceiling and wall making good, which can exceed the damper cost. Cleaning is priced by length or per system. Insulation repair is by length. Rebalancing is per floor or per system. Replacement of ductwork is usually carried in a fit-out or major plant project.

Fire damper works and testing are code compliance and recur; cleaning and repairs are repairs and maintenance; replacement is lifecycle; asbestos removal is code compliance.

• Australia. AS 4254.1 and 4254.2 cover flexible and rigid ductwork; AS 1668.1 covers fire and smoke control in ductwork; fire dampers are inspected and tested under AS 1851 as essential safety measures; AS/NZS 3666 covers hygiene.
• United Kingdom. BESA DW/144 specifies sheet metal ductwork; BESA TR/19 sets hygiene; fire dampers follow BS EN 15650 and are tested at least annually under BS 9999 guidance; Approved Document B.
• United States. SMACNA standards for ductwork; NFPA 90A for air conditioning systems; NFPA 80 and NFPA 105 require fire and smoke dampers to be tested one year after installation and then every four years (six in hospitals); NADCA ACR for duct cleaning.

Fire damper testing is commonly an annual certification item in all three countries.

• Fire and smoke damper register with test records and dates.
• Annual essential safety measures or fire safety statements covering dampers.
• Test and balance reports, original and after recent fit-outs.
• Duct hygiene inspection and cleaning records.
• Asbestos register.
• Mechanical as-built drawings showing ductwork and damper locations.
• Fit-out records showing changes to ductwork.