Spiral ducting is the backbone of a reliable ventilation system. Made from galvanised steel with a helical seam, it provides high rigidity, smooth internal surfaces and lower pressure drop than many alternatives. A bespoke cut-to-length service ensures each run fits the building precisely, which helps reduce leakage, installation time and rework.

Why choose spiral tube ducting

• Efficient airflow: The round profile and smooth interior reduce turbulence and friction, supporting lower fan energy for the same duty.
• Airtight joints: When paired with rubber-sealed couplers and fittings, systems can achieve high airtightness classes (often up to Class C) which cuts energy loss.
• Structural strength: The spiral seam increases stiffness, allowing wider support spacing compared with thin flex.
• Clean look: Suits exposed-duct designs in retail and hospitality when a neat industrial aesthetic is required.

Lengths, diameters and when to use 1.5 m vs 3 m

Buy Ventilation supplies 1.5 m and 3 m spiral tube sections as standard to balance transport, access and speed on site. Use this quick rule of thumb:

• 3 m lengths: Fewer joints, faster runs, ideal in open plant rooms and long corridors.
• 1.5 m lengths: Easier handling in tight risers, small lifts and retrofit jobs with limited access.

Common diameters range from 80 mm to 400+ mm. For extract branches and dMEV connections, smaller sizes are typical, while main trunks often step up to maintain sensible velocities.

Spec tips: pressure, velocity and noise

• Static pressure: Spiral systems are well suited to low- and medium-pressure building ventilation.
• Design velocity: Aim for 2–3 m/s in occupied rooms and 5–7 m/s in main ducts to balance size, noise and efficiency.
• Acoustics: Round ducting reduces breakout noise. Where needed, add lined silencers or increase diameter to lower velocity.

Fittings and compatibility

The system integrates with a full range of spiral fittings — bends, tees, reducers, saddles, end caps — manufactured to tight tolerances for a secure push-fit with slip couplers or quick clamps. Choose pressed bends for the lowest pressure loss where space allows; use segmented bends when tighter radii are unavoidable.

Browse Spiral Tube Ducting and matching Spiral Fittings to build a complete bill of materials.

Installation best practice

• Minimise joints: Use the longest practical lengths to cut leakage points.
• Seal correctly: Use rubber-gasketed couplers and tighten to manufacturer torque; apply approved sealant where specified.
• Support spacing: Follow load tables; typical spacing is around 2–3 m, closer for larger diameters or heavy ancillary items.
• Smooth airflow: Avoid hard 90° changes; keep at least 1–2 duct diameters of straight length before and after fans, filters and sensors.
• Corrosion and fire: Galvanised steel offers robust protection for most internal environments; insulate where required for condensation control and fire strategy.

Bespoke service: what you get

• Cut-to-length tubes to the nearest millimetre to match drawings and site dims.
• Factory-formed ends for quick coupling and airtight performance.
• Pre-selected fittings packs based on your schematic to reduce on-site guesswork.
• Labelling per run to speed installation and sign-off.

Compliance and documentation

A well designed spiral system supports compliance with Building Regulations Part F (ventilation) by delivering the specified design airflow with controlled leakage. Keep commissioning data, fan settings and as-built drawings together to streamline handover.

Next steps

Send us your layout or take-off and we will return a cut-list, fittings schedule and lead time. Start with our Spiral Tube Ducting (1.5 m & 3 m) and add compatible spiral fittings to complete the system.