Product Review: 125mm Condensation Trap with Overflow

Keeping ductwork dry and efficient

Condensation is one of those problems that can quietly cause big issues in a ventilation system. Moisture build-up inside ducting can lead to mould growth, corrosion, reduced airflow efficiency, and even water damage if it’s left unchecked. The 125mm Condensation Trap with Overflow is designed to prevent those problems by collecting and draining away excess moisture before it becomes an issue.
We’ve supplied these to commercial installers, commercial HVAC contractors, and even DIYers working on bathroom ventilation upgrades. They’re a simple but effective way to extend the life of your ducting and keep air quality at its best.

Why this condensation trap works so well

This model is suitable for 125mm round ducting, which is a common size for domestic extraction systems in bathrooms, toilets, and utility rooms. It’s built from flame-retardant polymer, making it safe for use in a variety of installations, and it’s lightweight, which makes fitting it quick and easy.

Key benefits:

• Prevents moisture damage – Stops water from travelling through the ducting and damaging fans or ceilings.
• Overflow outlet – Provides a way for excess water to escape safely if the trap fills up.
• Minimal airflow disruption – Designed to maintain smooth airflow with minimal turbulence.
• Easy to install – Push-fit connections make it simple to connect with duct fittings, extractor fans, or terminals.
• Durable build – Flame-retardant polymer construction for safety and long service life.

Where we’ve seen them used

• Bathroom extraction systems – Prevents steam from condensing and dripping back through the fan.
• Utility room ventilation – Handles moisture from tumble dryers or washing areas.
• Kitchen ducting – Stops grease-laden moisture from settling in duct runs.
• Commercial washrooms – Keeps high-use systems free from condensation issues.

One customer told us they fitted one after repeated ceiling stains from an old duct run and haven’t had a problem since.

Things to keep in mind

You’ll need straight pipe connectors if you’re joining two duct lengths on either side of the trap.
The overflow should be routed to a suitable drain point to ensure collected water is discharged safely.
It’s designed for horizontal installation in round duct runs, check your space before ordering.

Frequently Asked Questions

Q: What size ducting will this fit?

It’s designed for 125mm round ducting, which is common in domestic and light commercial ventilation.

Q: Does it affect airflow?

The internal design minimises turbulence, so it has little impact on system performance.

Q: Where should I install it?

It should be placed at a low point in the duct run where condensation is most likely to collect, with the overflow outlet connected to a drain.

Q: Can it be used in kitchen extract systems?

Yes, but regular cleaning is recommended if the system carries greasy air from cooking.

Q: What material is it made from?

Flame-retardant polymer, making it lightweight, safe, and easy to handle.

Written by Enya Kerry – Office Manager at Ducting Express

With over four years in ducting and ventilation systems, and W201 and P601 certifications, I help our customers choose components that keep their systems efficient, safe, and easy to maintain.