Spiral Ducting and Fittings
Galvanised spiral ducting and the complete matching fitting range, all in 24 standard diameters from 80mm to 1000mm. Spiral duct is the backbone of round ducted ventilation — rigid, airtight and economical — and this category holds everything needed to build a full system from a single order.
Browse the spiral range
- Spiral ducting — supplied in 3m lengths across all 24 diameters
- Bends and elbows — 30, 45, 60 and 90 degree angles
- T-pieces and Y-pieces — 45 and 90 degree branch fittings
- Reducers — over 160 diameter combinations
- Connectors and spigots — male, female and top hat
- Cap ends and terminals — cap ends, mesh terminals, bird beaks, jet cowls and weather hats
- Bracketry — split rings and suspension rings
- Access doors, circular silencers and roof flashings and cowls
One system, one size logic
Every fitting follows the same diameter series as the duct itself, so a 315mm system means 315mm bends, 315mm tees, 315mm connectors and 315mm split rings — no cross-referencing between incompatible ranges. The series covers 80, 100, 125, 150, 160, 180, 200, 224, 250, 280, 300, 315, 355, 400, 450, 500, 560, 600, 630, 710, 762, 800, 900 and 1000mm, which is why one order here can carry a system from a small extract branch to a full industrial main. Insulating duct wrap in 18m rolls is also available for lagging completed runs, and duct sealant, foil tape and tek screws live in our fasteners and accessories range next door.
Stocked items ordered by 3pm are despatched next day, and UK mainland delivery is free on orders over £400 ex VAT. For branching into existing duct without breaking the run, see the companion shoes and saddles range.
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Bends and Elbows
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Bracketry
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Cap End and Terminals
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Connectors and Spigots
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T-Pieces and Y-Pieces
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Roof Flashings and Cowls
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Access Door
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Reducers
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Silencers
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Spiral Ducting
What is Spiral Ducting?
Spiral ducting (also known as spiral wound ducting or tube ducting) is a type of round metal ductwork manufactured by spirally winding a continuous strip of galvanised steel into a rigid tube with a locked seam. This construction method produces ductwork that is inherently airtight, structurally strong, and cost-effective compared to rectangular alternatives.
Spiral duct uses approximately 32% less material than equivalent rectangular ducting for the same airflow capacity, making it both lighter and more economical. The round profile also creates less air resistance, resulting in lower pressure drops and reduced fan energy consumption over the life of the system.
Materials and Construction
Our standard spiral ducting is manufactured from 0.5mm to 1.0mm galvanised mild steel (gauge increases with diameter). The galvanised coating provides excellent corrosion resistance for most indoor applications. For environments requiring enhanced corrosion protection — such as swimming pools, coastal installations, or chemical processing — we can supply stainless steel spiral ducting to order.
All our spiral ductwork is manufactured to DW/144 standards, the industry specification for sheet metal ductwork in the UK. This ensures consistent quality, accurate sizing, and compatibility with standard fittings from any DW/144-compliant manufacturer.
Sizing Guide
Spiral ducting is measured by its inside diameter. Standard UK sizes range from 80mm up to 1000mm. Choosing the correct diameter depends on the required airflow rate and the acceptable air velocity for your application:
- 80mm to 150mm — Domestic extraction (bathrooms, utility rooms, cooker hoods)
- 160mm to 315mm — Commercial ventilation (offices, retail units, restaurants, kitchens)
- 355mm to 630mm — Industrial systems (warehouse ventilation, factory extraction, dust collection)
- 710mm to 1000mm — Large-scale industrial and plant room applications
Not sure which size you need? Use our Duct Sizing Calculator to find the recommended diameter based on your airflow requirements.
How Spiral Ducting Connects
Spiral duct has a female (plain) end on both sides. Fittings such as bends, T-pieces and reducers have a male (crimped) end that inserts into the duct. To join two lengths of straight duct together, you need a male coupler (also called a connector or joiner).
Joints should be sealed with duct sealant or foil tape and secured with self-tapping screws or pop rivets for a permanent, airtight connection. For accessible systems that may need future dismantling, we recommend using split clips instead of screws.
Installation and Bracketing
Spiral ducting should be supported with appropriate brackets at intervals of no more than 2 metres for horizontal runs. We stock a full range of duct brackets, split clips, and suspension fixings. Vertical runs require additional support at each joint and at regular intervals.
Why Choose Alpha Air?
Alpha Air has been manufacturing and supplying ducting and ventilation products. We hold extensive stock of all standard spiral ducting sizes and fittings, with over 90% of orders dispatched the same day. Our technical team can advise on sizing, specification, and system design — call us on 0116 246 0031.
Frequently Asked Questions
What diameter spiral ducting do I need?
The required diameter depends on your airflow rate and application. As a guide: 100-150mm for domestic extraction, 200-315mm for commercial ventilation, and 355mm+ for industrial systems. Use our Duct Sizing Calculator for a specific recommendation based on your airflow in litres per second or cubic metres per hour.
How do I connect two lengths of spiral ducting together?
You need a male coupler (connector). Spiral duct has female (plain) ends, so a male coupler with crimped ends inserts into each duct length to join them. Seal the joints with duct sealant or foil tape and secure with self-tapping screws or split clips.
Is spiral ducting measured by inside or outside diameter?
Spiral ducting is measured by its inside diameter. When you order 100mm spiral duct, the internal bore is 100mm. The outside diameter will be slightly larger depending on the material gauge (typically 1-2mm larger).
Can I cut spiral ducting to a shorter length?
Yes, spiral ducting can be cut to length on site using a metal cutting disc, jigsaw with a metal blade, or tin snips. Mark your cut line with tape for a clean, straight edge. File any sharp edges after cutting.
What is the difference between spiral and flexible ducting?
Spiral ducting is rigid, made from galvanised steel, and provides the best airflow performance with minimal pressure drop. Flexible ducting is a corrugated aluminium or insulated tube that bends easily but creates more air resistance. Use spiral for main runs and flexible only for short connections to grilles, fans, or diffusers.
Do you offer stainless steel spiral ducting?
Yes, we can supply stainless steel spiral ducting to order for applications requiring enhanced corrosion resistance, such as swimming pools, coastal environments, or chemical extraction. Contact our team on 0116 246 0031 for pricing and lead times.