What’s it made of?

The pipe is manufactured from white PVCu – a non-corrosive, fire-retardant plastic with good durability in both warm and cold environments. It’s UV-stabilised, which helps prevent yellowing if exposed to sunlight (useful in loft spaces with skylights or conservatories).

• Internal diameter: 125mm
• External diameter: 128mm
• Temperature range: −15°C to +60°C
• Finish: Gloss white, wipe-clean surface

How does it fit together?

Installation is straightforward. All 125mm ductwork fittings are designed with male spigots that slot directly into this duct pipe. You won’t need extra adaptors unless you're changing sizes. The push-fit connection is snug, but will require self drill screws to secure each joint, for long-term sealing we recommend a bead of ducting sealant followed by foil tape around the join. That keeps everything airtight and secure.

When would I use this ducting?

This 125mm pipe is a solid choice for a range of ventilation setups. It’s big enough to handle airflow from domestic kitchen extractors or bathroom fans with long duct runs, but not so bulky that it becomes awkward to route through joists or boxed-in corners. You’ll also see this size used in:

• MVHR (mechanical ventilation with heat recovery) systems
• Positive input ventilation (PIV) units
• Air conditioning pipework
• Utility room or downstairs WC fan vents

125mm Plastic Ducting – FAQs

- What is 125mm ducting typically used for?
This size is ideal for ventilation systems that need more airflow than smaller 100mm pipe can handle. It’s commonly used for bathroom extractor fans with long duct runs, domestic kitchen hoods, utility rooms, and some heat recovery or PIV units.
- Can I use this ducting with my domestic cooker hood?
Yes, many cooker hoods support 125mm ducting. Always check your hood’s specs first – some models work better with 150mm. If 125mm is compatible, it’s a good balance between airflow and compactness, especially in flats or smaller kitchens.
- How do I connect two lengths of 125mm pipe?
You’ll need a 125mm straight connector. The pipe ends slide into either side of the connector, and we recommend securing with self drill screws & sealing the joints with foil tape and duct sealant for an airtight finish.
- Is this ducting rigid or flexible?
This is rigid ducting – also called “solid” or “PVC” ducting. It holds its shape permanently and is better for long runs than flexible duct, which can sag and reduce airflow. If you need to bridge a short gap or add vibration isolation, you can use a short section of flexi.
- Do I need to insulate the ducting?
If you’re running this duct through cold spaces (like a loft or garage), yes – it’s best to insulate it to prevent condensation from forming inside. You can either wrap it with insulation or use pre-insulated duct if available.
- How long can I run 125mm ducting before performance drops?
There’s no fixed limit, but airflow starts to drop over longer distances, especially with bends. Try to keep runs under 6 metres if possible, and use gentle bends (not tight elbows). Rigid pipe like this helps minimise losses compared to flexi duct.
- Can I reduce or increase from 125mm to another size?
Yes – we stock reducers and increasers that allow you to transition between 100mm, 125mm, and 150mm duct sizes. This is useful if you’re connecting to a fan spigot or grille that doesn’t match the main duct run.

Need advice?

If you’re unsure whether 125mm is the right size for your project, or you want help picking the right fittings, our team’s always happy to help. You can give us a call, email, or chat online – we’ve been supplying plastic ducting for over a decade and know the common pitfalls. We’ll help you get it right first time.