Plastic Ducting

Rigid plastic ducting for domestic and light commercial ventilation — the clean, easy-to-install choice for extractor fans, cooker hoods, tumble dryers and bathroom extract runs. Alpha Air stocks both round plastic ducting and flat channel (low-profile) plastic ducting in all the standard UK sizes, with the full supporting cast of bends, tee pieces, couplers, clips, shutters and wall plates. Stocked items ordered by 3pm are despatched for next-day delivery.

Round or flat channel — which should I use?

Round plastic ducting moves the most air for its size and comes in 100mm, 125mm and 150mm diameters in 2m lengths — matching the spigot sizes of most domestic fans and cooker hoods. Use it wherever you have the space to run a round duct.

Flat channel plastic ducting is the low-profile alternative for tight spaces — above kitchen cupboards, inside bulkheads and under floors. It comes in three sizes, 110mm x 54mm, 204mm x 60mm and 220mm x 90mm, again in 2m lengths, with matching horizontal and vertical bends so the duct can turn flat or on edge without robbing headroom.

Need to switch between the two? Flat-to-round transformers — straight and angled — convert each flat channel size to the matching round diameter, so a fan with a round spigot can feed a flat channel run and vice versa.

Fittings for a complete run

Bends — 45 and 90 degree bends for round duct; horizontal, vertical and adjustable bends for flat channel

Tee pieces for branching, and couplers for joining straight lengths

Reducers for stepping round duct between diameters, including 150mm to 80mm cone reducers

Ducting clips to support runs neatly against walls and joists

In-line back draught shutters to stop cold air blowing back through idle ducts

Wall plates — plain or with spigot — for tidy terminations through external walls

Planning a plastic duct run

Start at the appliance: match the duct size to the fan or cooker hood spigot (100mm and 125mm are the common domestic sizes; high-output cooker hoods often need 150mm, and flat channel 204mm x 60mm carries a similar airflow to 125mm round in half the height). Keep the run as short and straight as the building allows — each bend adds resistance — and fit an in-line back draught shutter or a shuttered wall outlet on extract runs so cold air cannot blow back in when the fan is off. Couplers join 2m lengths cleanly, clips hold everything rigid, and a wall plate makes a neat, weather-tight finish where the duct exits the building.

Everything is sized to standard dimensions, so parts interchange with existing installations. If your project outgrows plastic — higher temperatures, larger diameters or commercial duty — step up to galvanised spiral ducting. UK mainland delivery is free on orders over £400 ex VAT.