Rectangular Ductwork — Made to Your Exact Size

Rectangular ductwork — often called square ductwork or box ductwork — is the workhorse of commercial ventilation. Its flat sides make the most of tight ceiling voids and riser shafts where circular duct simply won't fit, and we fabricate every section in our Hertfordshire workshop from galvanised sheet steel, folded, seamed and sealed to the DW144 specification.

There are no stock sizes: tell us the width, height and length you need — from small extract branches to 2000mm-wide supply trunking — and we make it to the millimetre. Configure any part online for an instant price, or send us your drawings for a full take-off.

The full rectangular range, from one workshop

• Straight lengths in any width, height and length
• Radius and square 90° / 45° bends and elbows
• Reducers, tapers and rectangular-to-round transitions
• Offsets (S-pieces), shoes, spigots and cravats
• Plenum / grille boxes, end caps, mez frames and louvres

Where rectangular duct is the right choice

Rectangular duct excels where space is the constraint: shallow ceiling voids in offices and schools, riser shafts in apartment blocks, and plant rooms where duct has to hug structure. A flat-sided duct can deliver the same air volume as a circular one at a fraction of the depth.

Built to DW144, checked before it leaves

Every section is fabricated to the DW144 sheet-metal specification: correct gauge for the duct size, beaded or cross-broken panels for stiffness, and oil-based mastic on every seam. Ends are protected with blue film before despatch so duct arrives clean and ready to hang.

Frequently asked questions

What sizes of rectangular ductwork can you manufacture?

Anything up to 2000mm wide, made to the exact millimetre — there are no fixed stock sizes. Common profiles like 400×200, 500×300 and 600×300 are all made to order alongside fully bespoke dimensions. If your project needs something larger, contact us and we'll fabricate it to suit.

Do you make square ductwork?

Yes — square ductwork is simply rectangular ductwork with equal sides, such as 300×300 or 500×500, and we fabricate it exactly the same way: made to order in galvanised steel to DW144, in any size up to 2000mm. Enter equal width and height in the online configurator for an instant price.

What connections do you supply on rectangular duct?

Each end can be specified independently: Mez flange for bolted joints, slip joints, or a raw edge if you're fitting flanges on site. Loose Mez frames are also available separately.

Is your rectangular ductwork DW144 compliant?

Yes — every section meets or exceeds DW144, with the correct sheet gauge for the duct size, stiffening beads or cross-breaking, and oil-based mastic sealed seams as standard.

How quickly can rectangular ductwork be delivered?

Because we fabricate in-house in Hertfordshire, made-to-order sections typically despatch within days rather than weeks, with delivery available UK-wide. Contact us with your programme dates and we'll confirm lead times.