After reviewing performance, material quality, installation practicality, and real-world suitability across the most commonly specified ducting options in the UK trade market, the best ducting for bathroom extractor fans in 2026 is: Domus Rigid PVC Round Duct, Domus Insulated Flexible Duct, Domus Flat Channel System, Systemair Circular Rigid Duct, Aluminium Flexible Ducting Hose, and Insulated Aluminium Flexible Duct.
Each one has a clear role in a well-specified bathroom extract system, and the right choice depends on your installation conditions.
Choosing the right ducting is just as important as choosing the right fan. A poor duct run can undermine even the best extractor fan, leading to condensation issues, mould complaints, and failed Building Regulations Part F inspections.
6 Best Ducting for Bathroom Extractor Fans: At A Glance?
Here is a quick overview of the six top-rated ducting options for bathroom extractor fans, ranked by our experts at eFans and assessed on material type, ideal application, and available sizes to help contractors and specifiers choose with confidence.
| Rank | Ducting | Type | Diameter | Best For |
|---|---|---|---|---|
| 1 | Domus Rigid PVC Round Duct | Rigid plastic | 100mm, 125mm, 150mm | Standard commercial and domestic extract runs |
| 2 | Domus Insulated Flexible Duct | Insulated flexible | 100mm, 125mm, 150mm | Loft and cold-space runs to prevent condensation |
| 3 | Domus Flat Channel System | Rigid PVC flat channel | 100mm, 125mm equivalents | Concealed runs in wall cavities and service voids |
| 4 | Systemair Circular Rigid Duct | Rigid steel/galvanised | 100mm–200mm | Commercial and higher-spec mechanical ventilation |
| 5 | Aluminium Flexible Ducting Hose | PVC-coated aluminium flexible | 100mm, 125mm, 150mm | Short, direct domestic extract runs |
| 6 | Insulated Aluminium Flexible Duct | Insulated aluminium flexible | 100mm, 125mm, 150mm | Fan-to-terminal connections in cold loft spaces |
6 Best Ducting for Bathroom Extractor Fans: Our Top Recommendations
The six ducting options below have been selected based on hands-on product knowledge, trade customer feedback, and performance in real-world bathroom extract installations across the UK.
1. Domus Rigid PVC Round Duct
Domus Rigid PVC Round Duct is the go-to choice for professional bathroom extract installations in the UK trade market, and it consistently sits at the top of the specification list for contractors who want a reliable, low-resistance solution across standard domestic and light-commercial bathroom runs.
Available in 100mm, 125mm, and 150mm diameters, it covers the full range of common bathroom extractor fan sizes and connects seamlessly with Domus' comprehensive range of fittings, bends, and terminal accessories.
The case for rigid PVC over flexible ducting in bathroom extract work is well established in the industry. Rigid duct maintains its circular cross-section throughout the run, which means airflow resistance stays consistent and predictable from one installation to the next.
Flexible duct, by contrast, can sag, kink, or compress if not installed carefully, and any restriction in the duct cross-section directly reduces the effective airflow the fan can deliver. Part F guidance actively recommends rigid ducting wherever it is practical to install.
Domus is one of the most trusted ventilation brands in the UK and is widely stocked by eFans across its full diameter range. The rigid round duct is manufactured from durable, smooth-bore PVC that resists moisture and corrosion, which matters in bathroom environments where moist, warm air is passing through the duct on every extraction cycle.
The smooth internal surface also reduces turbulence and noise compared to the corrugated inner wall of most flexible ducting products.
When to Use Domus Rigid PVC Round Duct for Your Project?
Choose Domus Rigid PVC Round Duct if...
-
You are installing a bathroom extract system in a new-build or significant refurbishment where the duct route can be planned and built in from the start
-
The Building Regulations Part F specification or a LABC / SAP assessor is requiring rigid ducting throughout the run
-
You want the lowest possible duct resistance for maximum fan performance and long-term reliability
Do not choose Domus Rigid PVC Round Duct if...
-
The installation is a retrofit in an occupied property with limited access, where breaking into walls or ceilings is not feasible
-
The duct route requires tight turns or unusual angles that are impractical to achieve with rigid fittings
-
Budget is very constrained and a short, low-resistance flexible run would adequately serve the application
2. Domus Insulated Flexible Duct
Domus Insulated Flexible Duct is the most important upgrade a contractor can make on any bathroom extract installation that runs through a loft, ceiling void, or other unheated space. The insulating layer wraps the duct in a thermal barrier that keeps the warm, moisture-laden air from the bathroom at a consistent temperature as it travels towards the external terminal, which prevents the condensation that forms inside uninsulated ductwork during colder weather.
Condensation inside duct runs is one of the most common problems in domestic bathroom ventilation across the UK, and it is almost entirely avoidable with the right choice of ducting at the specification stage.
When warm, humid extraction air hits a cold, uninsulated duct surface, moisture drops out of the air and collects in the lowest point of the duct. Over time that leads to water dripping back towards the fan, moisture appearing around ceiling roses, and in some cases visible water damage in the loft. Insulated flexible duct stops that cycle before it starts.
Domus Insulated Flexible Duct is available in 100mm, 125mm, and 150mm from eFans, and it is a product that experienced contractors tend to use as their default for any loft route rather than only specifying it when condensation has already become a problem.
The combination of a flexible core and an insulating jacket also means it handles the tight or awkward routing common in domestic loft spaces without compromising thermal performance.
When to Use Domus Insulated Flexible Duct for Your Project?
Choose Domus Insulated Flexible Duct if...
-
The bathroom extract duct route passes through a loft, roof space, or any other unheated void
-
You are installing in autumn or winter and cold-weather condensation risk is an immediate concern
-
The installation is in a flat or terrace where the duct may run through a shared cold zone before reaching an external terminal
Do not choose Domus Insulated Flexible Duct if...
-
The entire duct run is within the heated envelope of the building and condensation risk is genuinely minimal
-
The installation route is long and complex, where rigid duct would deliver better long-term airflow performance
-
The application is purely commercial and a purpose-specified commercial ducting system is required instead
3. Domus Flat Channel System
The Domus Flat Channel System gives contractors a rigid, low-profile ducting solution for bathroom extract installations where round duct simply will not fit. Flat channel profiles, typically 110x54mm for 100mm equivalent and 204x60mm for 125mm equivalent, sit neatly within service voids, behind skirting boards, inside stud walls, and above suspended ceilings in commercial washrooms and multi-occupancy residential buildings.
Where a round duct would either be visible or require significant structural disruption to conceal, flat channel solves the problem without compromise.
Domus flat channel ducting is manufactured from smooth-bore PVC, which keeps internal resistance low and the system easy to clean or inspect over its life. The flat channel range includes all the components needed for a complete installation, including 90-degree horizontal and vertical bends, offset pieces, in-line adaptors, and transition pieces to connect flat channel to round duct at the fan outlet or terminal end.
That system approach means every join is a designed fit rather than a forced one, which is important for both airtightness and compliance with Approved Document F.
For commercial bathroom ventilation in offices, retail units, schools, and healthcare buildings, flat channel ducting is often the only realistic option for achieving a clean, professional finish within the constraints of the building fabric. eFans stocks the full Domus flat channel system across 100mm and 125mm equivalents, including all fittings and adaptor pieces for complete system builds.
When to Use Domus Flat Channel for Your Project?
Choose Domus Flat Channel if...
-
The installation is in a commercial or residential building where round duct cannot be concealed without significant structural work
-
You are fitting within a stud wall, above a suspended ceiling, or in a service void with height restrictions
-
The specification requires a neat, professional finish with no visible ductwork in a washroom or en-suite corridor
Do not choose Domus Flat Channel if...
-
The duct run is in a loft or open ceiling void where round duct can be run freely without any visibility concerns
-
The project has a very long or complex duct route where flat channel's slightly higher equivalent resistance versus round duct could become a factor
-
The installation is a straightforward short run to an outside wall where round duct is the simpler, faster choice
4. Systemair Circular Rigid Duct
Systemair Circular Rigid Duct brings a higher-spec option to bathroom and general mechanical ventilation extract systems, particularly on commercial projects where the ducting forms part of a wider Systemair ventilation installation.
Available in 100mm, 125mm, 150mm, and 200mm, and manufactured from galvanised steel, Systemair rigid circular duct is built for demanding environments and continuous-duty applications where PVC alternatives may not meet the material specification.
In commercial washroom, healthcare, and education building projects, specifiers often require metallic ductwork to satisfy fire performance requirements or system specifications set by the M&E consultant. Systemair rigid duct fits those requirements directly and integrates without adaptation into the broader range of Systemair ventilation fans, silencers, and accessories stocked at eFans.
That design consistency across components reduces installation time and removes the risk of mismatched fittings causing airtightness failures.
For facilities managers overseeing large commercial buildings with multiple bathroom extract points, Systemair rigid duct also offers a practical maintenance advantage. Galvanised steel ductwork is easier to inspect, clean, and repair than flexible alternatives, and it retains its shape and performance characteristics throughout its service life without sagging or deforming under sustained airflow conditions.
When to Use Systemair Circular Rigid Duct for Your Project?
Choose Systemair Circular Rigid Duct if...
-
The project is commercial, healthcare, educational, or any building type where metallic ductwork is specified or preferred
-
The extract system is part of a larger Systemair ventilation installation and you want consistency across all duct and fan components
-
The application demands long-term durability, cleanability, and resistance to physical damage in a plant room or accessible ceiling void
Do not choose Systemair Circular Rigid Duct if...
-
The project is a straightforward domestic bathroom installation where PVC rigid or insulated flexible duct is the practical and cost-effective choice
-
Budget does not allow for the premium associated with metallic ductwork over equivalent PVC solutions
-
The duct route requires flexible connections and a rigid steel system is not practical throughout
5. Aluminium Flexible Ducting Hose
PVC-coated aluminium flexible ducting hose remains one of the most widely used products in domestic bathroom extract installations across the UK, and when it is used correctly it delivers a quick, practical, and effective solution for the majority of short residential duct runs.
The flexibility of the aluminium core makes it easy to route around joists, noggins, and other structural elements in ceiling voids and loft spaces without cutting or notching.
The product performs at its best when the run is kept short, pulled fully taut, and supported along its length to prevent sagging. Building on BSRIA BG 43 guidance and Part F recommendations, flexible duct should ideally be limited to 1.5 metres in any bathroom extract system, particularly where the duct connects the fan to the first rigid section or to an external terminal on a short outside-wall installation.
Aluminium flexible ducting hose is available from eFans in 100mm, 125mm, and 150mm, with matching jubilee hose clips, duct tape, and adaptor fittings to complete the installation. It is a product that most contractors carry on the van as a matter of course, and when it is used in the right circumstances rather than as a substitute for a properly designed rigid run, it delivers reliable results without fuss.
When to Use Aluminium Flexible Ducting Hose for Your Project?
Choose Aluminium Flexible Ducting Hose if...
-
The duct run is short, direct, and passes through a warm or conditioned space where condensation risk is low
-
You need to make a quick, neat connection from the fan outlet to the first rigid duct section or directly to a nearby external terminal
-
The installation is a domestic retrofit where access is limited and a flexible solution is the only practical option
Do not choose Aluminium Flexible Ducting Hose if...
-
The duct run exceeds more than a couple of metres, particularly through a cold loft where condensation inside the duct is a real risk
-
Building Regulations compliance requires rigid ducting throughout, as flexible runs will reduce effective airflow and may not pass inspection
-
The duct route involves multiple bends or changes in direction, where each restriction compounds the loss of airflow through the system
6. Insulated Aluminium Flexible Duct
Insulated aluminium flexible duct occupies a practical middle ground between standard flexible hose and full rigid insulated ducting, making it a popular choice for domestic bathroom extract jobs where the run passes through a cold space but full rigid installation is not straightforward.
The insulating jacket, typically mineral wool or foam, wraps around the aluminium core and prevents condensation forming inside the duct as warm bathroom air travels through a cold loft or ceiling void.
For short to medium loft runs of up to three to four metres on domestic properties, insulated aluminium flexible duct combines the thermal protection needed for cold-space routing with the installation flexibility that makes retrofit work manageable. It is supported, pulled taut, and sealed at both ends using foil tape and jubilee clips, giving a joined and thermally consistent system that reduces moisture risk without requiring full rigid installation.
eFans stocks insulated ducting in 100mm, 125mm, and 150mm, alongside the full range of Domus and Systemair fittings needed to connect it to rigid duct sections, fans, and external terminals. For contractors fitting bathroom fans in houses with cold, accessible loft spaces, having a reel of insulated flex on the van means the job is done right first time without needing a second visit for condensation callbacks.
When to Use Insulated Aluminium Flexible Duct for Your Project?
Choose Insulated Aluminium Flexible Duct if...
-
The duct run passes through a cold loft or unheated ceiling void and full rigid installation is not practical
-
The job is a domestic retrofit where installation simplicity and thermal protection both matter
-
You want to reduce the risk of cold-weather condensation callbacks on a bathroom extract installation
Do not choose Insulated Aluminium Flexible Duct if...
-
The duct run is entirely within the heated building envelope and condensation risk is genuinely not a factor
-
The installation is a commercial project where a rigid metallic ducting system is specified or required by the M&E consultant
-
The run exceeds four to five metres, where a properly planned rigid-and-insulated system would give significantly better long-term airflow performance
How Did We Assess the Best Ducting for Bathroom Extractor Fans?
Our assessment draws on eFans' direct experience supplying ventilation ducting to contractors, M&E consultants, facilities managers, and HVAC engineers across the UK.
eFans stocks over 119 ducting products including rigid plastic ducting, flexible ducting hose, flat channel systems, round duct, and all connectors, bends, adaptors, and tee pieces from leading brands including Domus and Systemair, available from 100mm to 200mm across PVC, aluminium, and insulated formats.
That range of stock, combined with day-to-day contact with trade customers solving real installation problems, informs every recommendation on this list.
The criteria used to assess the best ducting for bathroom extractor fans are as follows:
-
Airflow resistance: Ducting that maintains a low, consistent resistance throughout the run performs better in practice. Smooth-bore rigid duct consistently outperforms corrugated flexible alternatives on this measure, particularly over longer runs.
-
Condensation management: Any ducting specified for runs through cold lofts, roof spaces, or unheated voids was assessed on its ability to prevent condensation forming inside the duct, one of the most common causes of bathroom extract failure in UK properties.
-
Building Regulations Part F compliance: All ducting reviewed here is compatible with the requirements of Approved Document F. We considered how each product type performs under inspection and commissioning conditions, including flow rate verification.
-
Installation practicality: We assessed how realistic each ducting type is to install across both new-build and retrofit scenarios, recognising that the most technically correct solution is not always the most practical one on a constrained domestic job.
-
Material durability: Moisture resistance, dimensional stability, and resistance to deformation over time were considered for each material type, particularly relevant for PVC and aluminium products in warm, humid extraction environments.
-
System compatibility: Ducting that integrates neatly with a full range of bends, adaptors, flat channel transitions, and external terminals received higher marks, as a complete system approach reduces the risk of poorly matched joints and airtightness failures.
-
Brand support and availability: All ducting featured here is stocked by eFans with fast UK delivery, backed by brands with strong technical documentation and trade support, which matters when you need to spec a job quickly and order with confidence.
How to Choose the Best Ducting for Bathroom Extractor Fans for Your Project?
Getting the ducting right is the part of a bathroom extract installation that has the biggest impact on long-term system performance, yet it is the part most often treated as an afterthought.
Selecting the right duct material, diameter, and configuration from the start reduces callbacks, supports Building Regulations compliance, and means the fan you have specified actually delivers the airflow it is rated for.
Rigid vs Flexible Ducting for Bathroom Extract
Rigid ducting consistently outperforms flexible in terms of airflow resistance, because it maintains a consistent circular cross-section throughout the run with no sagging, kinking, or compression.
Approved Document F guidance and BSRIA BG 43 both recommend the use of rigid ducting wherever it is practically possible, with flexible duct limited to short connections of no more than 1.5 metres, typically at the fan outlet or the terminal end.
Flexible ducting remains useful and widely used on domestic retrofit installations where access constraints make rigid impractical. When flexible is used, it must be pulled fully taut, properly supported, and connected with tight jubilee clips and foil tape at each joint.
A sagging or kinked flexible run can reduce effective airflow by 25 to 50 percent in some configurations, which is the difference between a compliant and a non-compliant ventilation system under Part F.
The Right Duct Diameter for Bathroom Fans
Most domestic bathroom extractor fans use 100mm ducting as their standard outlet diameter, and 100mm rigid or flexible duct is the correct choice for the vast majority of single-room domestic bathroom extract installations.
Boosted or higher-output fans, particularly those serving larger bathrooms or those specified for continuous running in MEV systems, may use 125mm ductwork to reduce resistance and support the higher airflow rates those systems deliver.
Using undersized ducting is a common mistake that reduces fan performance and can cause the motor to work harder than it was designed to, shortening service life. Always check the fan manufacturer's recommended duct diameter before ordering, and size the full duct run to match rather than reducing or increasing diameter partway through unless a designed transition piece is used.
Insulated vs Uninsulated Ducting
Whether to use insulated ducting comes down almost entirely to the route the duct takes through the building. Any section of duct that passes through an unheated space such as a loft, roof void, external wall cavity, or sub-floor should be insulated.
Warm, moisture-laden extraction air from a bathroom will cool rapidly in a cold duct, causing condensation to form on the internal surface and collect in low points of the run.
In the UK, where loft-routed bathroom extract is standard in millions of houses built before 2000, condensation in uninsulated flex is one of the most frequent ventilation complaints. Specifying insulated flexible duct or wrapping rigid duct sections in lagging from the start is far less costly than investigating and rectifying a condensation problem after the installation is complete and decorated.
Flat Channel vs Round Duct
The choice between flat channel and round duct is mainly determined by the space available in the installation. Round duct is the most efficient shape for moving air with the lowest resistance, and it is the default choice wherever it can be concealed or where aesthetics are not a concern.
Flat channel is specified when the duct must fit within a wall cavity, run under a floor, or be hidden behind a service panel in a commercial washroom or en-suite corridor.
Flat channel ducting has a slightly higher resistance than round duct of the same equivalent diameter because the rectangular cross-section creates more surface friction per unit of airflow. That is not a significant problem on short or medium runs, but on longer flat channel runs it is worth accounting for in the fan selection to ensure the specified airflow is still achievable against the higher system resistance.
Fittings, Bends, and System Airtightness
Every fitting, bend, adaptor, and transition piece in a bathroom extract duct run adds resistance and creates a potential airtightness failure point. Each 90-degree bend is equivalent to approximately 1.5 metres of straight duct in terms of pressure resistance, which adds up quickly on an installation with three or four changes of direction.
eFans stocks a full range of Domus and Systemair bends, adaptors, tee pieces, and fan connectors in 100mm, 125mm, 150mm, and 200mm, covering both round and flat channel systems.
Using a matched system of fittings from the same brand range, rather than mixing components from different manufacturers, is the single most effective way to ensure tight, consistent joints that do not leak air or introduce unnecessary turbulence into the extract system.
Building Regulations Part F and Compliance
Building Regulations Approved Document F requires domestic bathrooms to achieve a minimum intermittent extract rate of 15 litres per second, with a continuous low rate of 8 l/s where the system operates continuously.
The duct run design directly determines whether the installed fan can meet those figures under real operating conditions, as resistance from long runs, multiple bends, and poor fitting joints all reduce effective airflow below the fan's rated output.
For new-build projects and notifiable refurbishments, the as-installed flow rate must be tested and verified for Building Control sign-off. Rigid ducting, proper insulation in cold spaces, matched system fittings, and correct fan sizing all contribute to passing that test without remedial work.
eFans supplies the full ducting system needed to build a Part F compliant bathroom extract installation, from fan outlet to external terminal.
Frequently Asked Questions
Can you use flexible ducting for a bathroom extractor fan?
Yes, flexible ducting can be used for bathroom extractor fans, but it should be used correctly and only where it genuinely suits the installation. Flexible duct works best on short, direct runs of no more than 1.5 metres, typically as a connection between the fan outlet and the first section of rigid ducting.
It must be pulled fully taut, properly supported, and sealed at both ends with foil tape and jubilee clips. Where the run passes through a cold loft or unheated space, insulated flexible ducting should always be used to prevent condensation forming inside the duct.
For longer or more complex routes, rigid PVC ducting will deliver significantly better airflow performance and is preferred under Approved Document F guidance.
What diameter ducting do I need for a bathroom extractor fan?
Most standard domestic bathroom extractor fans use a 100mm duct outlet and require 100mm ducting throughout the run. Some higher-output fans, particularly those used in MEV systems or larger bathrooms, use 125mm ductwork to support higher airflow rates with lower resistance.
Always check the fan manufacturer's specified duct diameter before ordering, as using undersized ducting increases system resistance and reduces effective airflow below the fan's rated output. Mixing duct diameters mid-run is not recommended unless a proper designed transition adaptor is used.
Does bathroom extractor fan ducting need to be insulated?
Bathroom extractor fan ducting must be insulated wherever the duct run passes through an unheated space, such as a loft, roof void, or cold ceiling void. Warm, moisture-laden extraction air cools rapidly inside uninsulated ductwork in cold spaces, causing condensation to form on the internal surface.
That condensation collects in low points of the run, can drip back towards the fan, and over time causes moisture damage in the surrounding structure. In the UK, where loft-routed bathroom extract is common in pre-2000 housing stock, insulated flexible ducting or insulated rigid ducting is the recommended choice for any section of duct outside the heated building envelope.
How many bends can a bathroom extractor fan duct have?
The fewer bends, the better. Each 90-degree bend adds approximately 10 Pa of resistance to the system, equivalent to around 1.5 metres of straight duct. A bathroom extract run with three bends, four metres of ductwork, and an external grille can lose 35 to 50 percent of the fan's effective airflow compared to its free-air rating.
Building Regulations Part F flow rate requirements must be met at the installed fan under actual duct conditions, not just at the fan's rated output, so every additional bend must be factored into the fan selection. If the duct route unavoidably includes three or more bends, choose a fan with a higher rated static pressure capability to compensate for the increased system resistance.
What is the difference between round duct and flat channel ducting for bathrooms?
Round ducting is the most aerodynamically efficient duct shape, delivering the lowest resistance for a given equivalent diameter and is the standard choice for bathroom extract wherever it can be installed without visibility concerns.
Flat channel ducting is a rectangular-profile alternative designed for installations where space constraints make round duct impractical, such as within stud walls, above suspended ceilings, or inside shallow service voids in commercial washrooms and en-suite corridors.
Flat channel has a slightly higher equivalent resistance than round duct due to greater surface friction per unit of airflow, which should be accounted for in the fan selection on longer flat channel runs. Both types are available from eFans in standard sizes with a full range of matching bends, adaptors, and transition pieces for complete system builds.
Do bathroom extract ducts need to be airtight?
Yes, all bathroom extract duct joints must be sealed to prevent air leakage, which reduces effective airflow and can allow moist extraction air to escape into the building fabric rather than being discharged outside. Approved Document F requires that ductwork for mechanical extract ventilation is sealed to prevent significant air leakage.
In practice, this means every joint between duct sections, bends, and fittings must be sealed with foil tape or mastic sealant appropriate to the duct material, with all flexible connections secured using jubilee clips. Using a matched system of fittings from a single brand range, such as the Domus or Systemair system ranges stocked at eFans, reduces the risk of gaps at connection points that are difficult to seal effectively.