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Coupling

Galvanised steel duct couplings for airtight ventilation

A duct coupling joins two flexible ducts of the same diameter through a cylindrical sleeve of galvanised sheet steel. The zinc coating resists corrosion in the humid conditions typical of indoor grow spaces, while the smooth interior wall maintains unrestricted airflow. Six diameters from 100 mm to 250 mm cover every setup, from compact hobby tent to professional installation.

Slide the duct at least five centimetres over each end of the coupling and secure both sides with a hose clamp for a fully airtight seal. A properly fitted coupling ensures your extractor retains its full capacity with no unnecessary pressure loss. Fast delivery throughout Belgium.

There are 6 products.

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Coupling 100 mm

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Coupling 125 mm

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Out-of-Stock

Coupling 150 mm

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Coupling 160 mm

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Coupling 200 mm

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Coupling 250 mm

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Duct couplings for your ventilation system

The duct coupling is the simple but essential component that joins two ventilation ducts of the same diameter into a hermetically sealed connection. Without a proper coupling, you are left with improvised solutions — tape and wrap — that come loose within weeks under motor vibration and constant negative pressure. A galvanised steel coupling costs a few euros, lasts for years and prevents any airflow loss at the joint. See also our duct clamps for a complete leak-free system.

Galvanised steel: why this material?

Our duct couplings are rolled from a single piece of galvanised sheet steel, with a lap-seam that leaves a smooth cylindrical surface. The zinc coating brings two key advantages for grow room use. First: corrosion resistance. Humidity in a flowering room sits between 40 and 60 percent, peaking briefly above 70 percent during irrigation. Plain steel would develop surface rust within months and spread it through the air circuit. Galvanised steel stays intact for years. Second: the smooth inner wall. Unlike aluminium flex ducting, a galvanised steel coupling has a perfectly flat interior without ribs, letting air flow through without turbulence. Over a single coupling the impact is small, but with multiple couplings in series it prevents significant cumulative pressure drop.

Six diameters for every standard configuration

Choose a coupling that matches the diameter of your ducting and equipment exactly. All six sizes are in stock:

Coupling 100 mm — for small hobby setups and compact fans
Coupling 125 mm — the most common size for standard grow tents
Coupling 150 mm — for mid-range extractors
Coupling 160 mm — for 120×120 cm tents with 400-550 m³/h fans
Coupling 200 mm — for larger tents and extractors up to 800 m³/h
Coupling 250 mm — professional installations above 1000 m³/h

Not sure which size to pick? Measure the inner diameter of your ducting with a calliper — that is the metric manufacturers use. Note: an insulated Sono-Connect has the same inner diameter as an Alu-Dec of the same nominal size; the insulation layer sits on the outside.

Applications and combinations

A duct coupling is useful in several scenarios. The most obvious: extending an existing duct when the original length is not enough — for example when your extractor fan and carbon filter are further apart than a standard duct allows. It also simplifies maintenance: replacing an old duct without dismantling the whole installation. The coupling lets you cut out the damaged section between two pieces of equipment and splice in a new duct. For wall pass-throughs, combine the coupling with a bushing — the coupling on the inside joins the duct to the bushing, and the clamp provides the seal.

Installation in three steps

Installation is straightforward but requires attention to detail. Step one: fully stretch both ducts — a compressed duct sits tighter and creates turbulence. Step two: slide each duct at least five centimetres over the steel end of the coupling. Any less and the risk of disengagement under pressure becomes too high. Step three: position a hose clamp directly over the overlap area (not on bare steel) and tighten firmly. Test the seal by running your palm along the joint while the system runs — no air flow should be perceptible. For extra security on critical connections, apply a layer of aluminium tape around the duct before tightening the clamp.

FAQ - Frequently asked questions about duct couplings

What is the difference between a coupling and a bushing?

A coupling joins two ducts together — it sits inside the air circuit between two duct sections. A bushing is a wall pass-through mounted through a panel, to which you then connect a single duct. The two products complement each other: use a bushing where air has to cross a partition, a coupling where two ducts have to be joined.

Can I use a coupling to join ducts of different diameters?

No, a coupling is for ducts of the same diameter. For joining different diameters, use a duct reducer, which has two ends of different sizes (for example 160 to 125 mm).

How much duct should I slide onto the coupling?

At least five centimetres on each side. Any less and the clamp does not have enough surface to hold the duct firmly, which risks disengagement under vacuum pressure or vibration. Seven to ten centimetres gives extra safety for permanent installations.

Should I use aluminium tape with a coupling?

Not essential — a properly fitted combination of duct, coupling and clamp is already airtight. Recommended for critical connections (carbon filter outlet, pass-through to the outside) and when you are unsure about older material that may have micro-cracks. A layer of tape around the duct before tightening the clamp adds an extra sealing barrier.

Does galvanised steel rust in a humid grow room?

The zinc coating protects the underlying steel for years, even at relative humidity up to 70 percent. In normal grow use, you would not expect visible corrosion for at least five to ten years. If surface rust does appear over time, it is usually confined to the visible outside and does not affect airflow function.

Order your duct coupling today at Plant & Flower. Fast, discreet delivery anywhere in Belgium.