110mm x 54mm rectangular ducting, also called flat ducting, flat channel ducting or System 100, is a low-profile rigid PVC ductwork system equivalent in airflow to a 100mm round duct. The flat rectangular profile routes through ceiling voids, kitchen unit plinths, stud walls and service risers with far less intrusion than round ducting, which is why it's the default choice for UK domestic kitchen extract, bathroom extract, and tumble dryer runs where space is tight.
We stock the full Domus System 100 range in 110x54mm: 2m straight lengths, 90° horizontal and vertical bends, 45° horizontal and vertical bends, T-pieces, straight connectors (plain and with damper), duct clips, round-to-rectangular adapters, and DFS110 fire sleeves for fire compartment penetrations. Every item in the System 100 range is cross-compatible, so you can build a complete rectangular extract from fan or cooker hood to external cowl. Email hello@efans.co.uk or call 0161 399 3825 for help with a parts list. Use the buttons below to filter by part type.
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Frequently asked questions
What is 110mm x 54mm ducting?
110mm x 54mm is a standard UK size of rigid rectangular PVC ducting, part of the Domus System 100 range. The "System 100" name reflects that it's airflow-equivalent to 100mm round ducting, which is the standard diameter for most domestic extract fans, cooker hoods and bathroom fans. The flat rectangular cross-section means the same airflow moves through a far shallower void, only 54mm deep, so the duct fits into spaces where a 100mm round pipe would not. That's why it's the go-to for running ducting through floor joists, over kitchen wall units, inside stud walls and through ceiling voids with minimal intrusion.
What is 110mm x 54mm ducting used for?
The most common uses are kitchen cooker hood extract, bathroom and toilet extract fans, utility room and tumble dryer extract, and MVHR supply or extract branches where a flat profile routes more cleanly than round. It's specified in new-build and renovation projects where the extract fan is a 100mm (4 inch) unit and the duct run needs to cross a ceiling void, rise through a stud wall, or drop behind kitchen units. For airflow volumes equivalent to 125mm or 150mm round ducting, step up to 204x60mm or 220x90mm.
Is 110mm x 54mm ducting the same as 100mm round?
Airflow-equivalent, yes. The 110x54 cross-sectional area is designed to match 100mm round ducting, so a 100mm extract fan or cooker hood can be run in 110x54 flat duct without significantly reducing performance. Physically they're different shapes, so you need a round-to-rectangular adapter (Domus DD070, in stock) to transition between the two, typically used at the fan or cowl end of the run. The rectangular duct itself is 110mm wide by 54mm deep externally.
What's in the Domus System 100 110x54 range?
The full System 100 range in 110x54 covers everything needed for a complete extract run: 2m straight duct lengths, 90° bends in both horizontal and vertical orientations, 45° bends in both orientations, T-pieces for branched runs, straight connectors to join two duct lengths, connectors with integral dampers, round-to-rectangular adapters (110x54 to 100mm round), duct clips for fixing to joists or walls, and DFS110 fire sleeves for sealed penetrations through fire compartment walls and floors. All parts are push-fit with a neoprene gasket for airtight joints.
How do I connect 110x54 ducting to a cooker hood or extract fan?
Most cooker hoods and extract fans have a 100mm (or 125mm/150mm) round spigot, not a rectangular one. Use a round-to-rectangular adapter (Domus DD070 for 110x54 to 100mm round) as the first connection at the fan: the round side fits onto the fan spigot, the rectangular side accepts the 110x54 duct. From there, run in 110x54 rigid PVC with bends and connectors as needed, and typically finish with another round-to-rectangular adapter before a round external cowl or wall kit. Some cooker hoods have a direct rectangular 110x54 outlet option, so check the hood's installation spec.
How do I join 110x54 ducting sections?
The Domus System 100 range is push-fit. Straight connector pieces (DD020, or DD027 with damper) join two lengths of 110x54 duct end-to-end. Bends and T-pieces have integral push-fit sockets at each end. For an airtight seal, important for MVHR and Building Regs extract, apply a bead of duct sealant inside the socket before pushing the duct home, then foil-tape over the joint externally. Fix runs every 600 to 800mm with the Domus 122-4 duct clip to stop deflection and reduce noise transmission.
Do I need a fire sleeve on 110x54 ducting?
If the duct passes through a fire-rated wall, floor or compartment boundary, yes. Building Regulations require that any penetration through a fire compartment is sealed to maintain the fire rating, as an unsealed duct creates a route for fire and smoke between compartments. The Domus DFS110 fire sleeve is designed to fit the 110x54 profile: it wraps around the duct at the penetration point and, in a fire, the intumescent material expands to close the opening. Common use cases are apartment extract risers, maisonette extract passing between floors, and any extract run crossing a fire-rated partition in flats or HMOs.
What's the maximum run length for 110x54 ducting?
For a 100mm extract fan, the manufacturer's installation guide typically allows a maximum total equivalent run length of 6 to 12m, depending on fan model. Every bend in the run counts as additional equivalent length: a 90° bend is typically equivalent to around 1m of straight duct, a 45° bend around 0.5m. Keep runs as short as possible, minimise bends, and where a long run is needed consider specifying a stronger fan or stepping up to 204x60 for lower pressure loss. Always check the specific fan or cooker hood spec sheet for its maximum permitted duct length.
