Plastic Circular Ducting Reducer – 125mm – 100mm

Round plastic ducting comes in 100mm, 125mm and 150mm diameters — matching the most common domestic fan spigot sizes of 4, 5 and 6 inches. Flat channel ducting comes in three sizes: 110×54mm, 204×60mm and 220×90mm. Each size has its own matching fittings, including bends, tee pieces, couplers, clips and wall plates, so you can build a complete run in one size.

All straight plastic ducting — round and flat channel — is supplied in 2 metre lengths. It cuts cleanly to length with a fine-tooth saw, so one length often covers a short kitchen or bathroom run, and longer runs are made by joining lengths with the matching couplers. Fittings such as bends and tee pieces are sold individually alongside the duct.

Round ducting offers the best airflow for a given size and is the first choice where space allows. Flat channel ducting is designed for tight spaces — above kitchen cupboards, in shallow ceiling voids or where a slim profile matters. If your fan or appliance has a round spigot, flat-to-round transformers, in straight and angled versions, let you switch between the two within the same run.

The system is push-fit: straight lengths join to bends, tees and transformers using the matching couplers and connectors for each size, and runs are held in place with ducting clips screwed to the wall or ceiling. For extract runs, joints can be taped or sealed for extra airtightness. No specialist tools are needed — cutting to length and screwing clips into place is all the fitting the system requires.

Rigid plastic ducting is the standard choice for domestic extract runs — kitchen cooker hoods, bathroom extractor fans, utility rooms and tumble dryer venting. A back draught shutter is worth adding on runs to an outside wall: it opens when the fan runs and closes when it stops, preventing cold outside air blowing back through the duct. We stock shutters for both round and flat channel systems.