Ducting and Fittings
Galvanised steel ducting and fittings for commercial and industrial ventilation, dust extraction and air movement systems. Alpha Air is a Leicester-based UK supplier stocking one of the most complete ranges of spiral ducting online, with 24 standard diameters from 3 inch to 40 inch and every fitting you need to go with it — bends, T-pieces, Y-pieces, reducers, connectors, cap ends, terminals, saddles and support bracketry.
What is spiral ducting?
Spiral ducting (also called spiral tube or spiro duct) is round galvanised steel duct formed with a continuous spiral seam, giving a rigid, airtight and cost-effective duct run. It is the standard choice for HVAC supply and extract systems, kitchen extract, dust and fume extraction, and general industrial ventilation. Our spiral ducting is supplied in 3m lengths across all 24 diameters — 3 inch, 4 inch, 5 inch, 6 inch, 6 inch, 7 inch, 8 inch, 9 inch, 10 inch, 11 inch, 12 inch, 12½ inch, 14 inch, 16 inch, 18 inch, 20 inch, 22 inch, 24 inch, 25 inch, 28 inch, 30 inch, 32 inch, 36 inch and 40 inch.
Which fittings do you stock?
Every part of a round ducted system is covered, in sizes to match the ducting:
- Bends and elbows in 30, 45, 60 and 90 degree angles, from 3 inch to 40 inch diameter
- T-pieces and Y-pieces for branching duct runs, including 45 degree and 90 degree tees
- Reducers — over 160 size combinations for stepping between duct diameters
- Male and female connectors and top hat spigots for joining duct and connecting to plenums
- Cap ends and terminals — cap ends (plain or with mesh), bird beaks, jet cowls and weather hats for terminating runs outside
- Shoes and saddles — flat shoes, 45 degree pipe saddles, 90 degree pressed saddles and curved boots for cutting branches into existing duct
- Bracketry — split rings and suspension rings for supporting duct runs
- Access doors for round duct (4 inch to 20 inch), circular silencers and Master Flash roof flashings to finish the installation
How do I put a spiral duct system together?
A typical run uses 3m lengths of spiral duct joined with male connectors, with bends turning the run where needed and T-pieces or Y-pieces splitting off branches. Reducers step the diameter down as airflow is distributed, saddles and shoes let you cut a branch into an existing duct without dismantling it, and split rings or suspension rings carry the weight back to the structure on threaded rod. At the end of the run, a cap end closes the duct off, while a jet cowl, weather hat or mesh terminal finishes an external discharge. Because we offer all 24 diameters and every fitting in matching sizes, you can specify the whole system in one order — the same 9 inch duct, 9 inch bends, 9 inch tees and 9 inch split rings, with nothing left to hunt down elsewhere.
Fast delivery from UK stock
Stocked ducting and fittings ordered before 3pm are despatched for next-day delivery, and UK mainland delivery is free on orders over £400 ex VAT. Made-to-order items show their lead time on the product page, so you always know where you stand before you buy.
Start with spiral ducting and fittings or jump straight to shoes and saddles. If you need rectangular ductwork made to size, see our bespoke rectangular ducting and fittings, or for clip-together extraction ducting see the Nordfab QuickFit range.
Complete Ductwork Solutions
Alpha Air supplies the full range of ducting and fittings needed to design, install, and maintain ventilation systems of any size. Whether you are fitting a simple kitchen extractor duct in a residential property or installing a multi-zone commercial HVAC system, we have the products and expertise to support your project.
Our Ducting Range
Our ducting range includes:
- Spiral Ducting and Fittings — Round galvanised steel ductwork in sizes from 80mm to 1000mm, plus the full range of bends, T-pieces, reducers, connectors, and brackets
- Reducers — Concentric and eccentric reducers for transitioning between duct sizes
- Roof Flashings and Cowls — Weatherproof terminations for ductwork penetrating through flat and pitched roofs
- Shoes and Saddles — Branch take-off fittings for connecting smaller ducts to larger main ducts
- Dampers — Fire dampers, volume control dampers, and non-return dampers for safety and airflow regulation
Materials and Standards
All our ductwork is manufactured from galvanised mild steel to DW/144 standards, ensuring compatibility, quality, and durability. Galvanised steel provides excellent corrosion resistance for indoor applications and is the industry standard for commercial and industrial ventilation ductwork in the UK.
For specialist applications, we can source stainless steel, aluminium, and PVC ducting to order. Contact our technical team to discuss your requirements.
Why Choose Alpha Air?
With many years in business and extensive stock held at our Leicester warehouse, Alpha Air is a one-stop shop for ductwork and ventilation supplies. We manufacture many of our products in-house, giving us control over quality and lead times. Over 90% of orders placed before 3pm are dispatched the same day. Free delivery on all orders over £400.
Frequently Asked Questions
What standard is your ducting manufactured to?
All our galvanised steel ducting is manufactured to DW/144, the UK industry specification for sheet metal ductwork. This standard covers material grades, gauges, construction methods, and tolerances, ensuring our products are compatible with any DW/144-compliant system.
Do you supply rectangular ducting?
We specialise in spiral (round) ducting and fittings, which is the most common and cost-effective ductwork type. For rectangular ducting requirements, please contact our team on 0116 246 0031 to discuss your project — we can source rectangular sections to order.
Can you help me design a duct system?
Yes. Our experienced technical team can advise on duct sizing, layout, component selection, and system design. We can review your drawings and provide a complete bill of materials with pricing. Call us on 0116 246 0031 or email sales@alphaair.co.uk with your project details.