204mm x 60mm Rectangular Ducting

Frequently asked questions

What is 204mm x 60mm ducting?

204mm x 60mm is a standard UK size of rigid rectangular PVC ducting, part of the Domus Supertube System 125 range. The "System 125" name reflects that it's airflow-equivalent to 125mm round ducting, the standard diameter for larger kitchen cooker hoods, heavy-use bathroom extract, and MVHR branches serving multiple rooms. The flat rectangular cross-section, 204mm wide by 60mm deep, routes through ceiling voids, behind kitchen units and through stud walls where a 125mm round duct would not physically fit.

What is 204mm x 60mm ducting used for?

Main uses are kitchen cooker hood extract where the hood has a 125mm spigot, larger utility or multi-room bathroom extract, and MVHR supply or extract branches where the airflow volume is above the 110x54 System 100 comfort zone. It's also used as the intermediate size on MVHR installations where the trunk runs in 220x90 and branches step down to 204x60 before the terminal. For 100mm fans step down to 110x54; for 150mm fans and MVHR trunks step up to 220x90.

Is 204mm x 60mm ducting the same as 125mm round?

Airflow-equivalent, yes. The 204x60 cross-sectional area is designed to match 125mm round ducting, so a 125mm extract fan or cooker hood performs similarly to a 125mm round run. Physically they're different shapes, so a round-to-rectangular adapter (Domus 570, 204x60 to 125mm, in stock) is needed to transition between the two, typically used at the fan or cowl end of the run. The rectangular duct itself is 204mm wide by 60mm deep externally.

What's in the Domus Supertube 204x60 range?

The full Supertube range in 204x60: 2m straight lengths, 90° bends in both horizontal and vertical orientations, 45° bends in both orientations, T-pieces for branched runs, straight connectors, 300mm universal connectors for offset joints, 440 and 441 elbow bends with fixed or rotating round spigots (for direct connection to 125mm fans and cowls), round-to-rectangular adapters (204x60 to 125mm), 3m flexible Supertube hose for final connections where rigid won't route, thermal insulated bends and T-pieces for use in cold lofts and roof voids, Supertube end caps, and DFS204 fire sleeves.

Do I need thermal insulated 204x60 parts?

For MVHR installations where the duct runs through cold spaces, typically unheated lofts and roof voids, yes. Warm extract air in a cold duct causes condensation inside the duct, which pools, drips, and over time damages the fan and ceilings below. The Domus thermal Supertube range (TS-coded parts, in stock) wraps the bends and T-pieces in insulation to keep the duct surface warmer than the dewpoint. Use insulated fittings wherever 204x60 duct passes through an unheated space, and wrap straight runs separately with pipe insulation or foil-backed mineral wool. For warm-void runs inside the thermal envelope, standard uninsulated parts are fine.

Can I use flexible 204x60 hose instead of rigid?

The Domus 533 Supertube 3m flexible hose is designed for short connections where a rigid bend won't route, typically at the fan or cooker hood end, or to absorb slight misalignment between duct sections. It should not be used for main duct runs. Flexible duct has significantly higher pressure loss than rigid and its corrugated internal wall traps dust, grease and moisture. Keep flexible sections short, under 1m where possible, pulled taut, and always transition to rigid Supertube for the main run.

How do I join 204x60 Supertube sections?

Supertube uses push-fit joints. Straight connectors (DD520, or the 5B303 universal 300mm version for offset joints) join two lengths end-to-end. Bends and T-pieces have integral push-fit sockets. For airtight joints, essential on MVHR and Building Regs extract, apply duct sealant inside the socket before pushing the duct home, then foil-tape over the joint externally. Fix horizontal runs every 600 to 800mm to stop sag and reduce noise.

Do I need a fire sleeve on 204x60 ducting?

Yes, wherever the duct penetrates a fire-rated wall, floor or compartment boundary. Building Regulations require sealed penetrations to maintain the fire rating, as an unsealed duct creates a smoke and fire spread path between compartments. The Domus DFS204 fire sleeve fits the 204x60 profile and contains intumescent material that expands during a fire to close the opening. Common use cases are apartment and HMO extract risers, multi-occupancy kitchen extract, and MVHR trunk lines crossing fire-rated partitions.

What's the maximum run length for 204x60 ducting?

For a 125mm extract fan or cooker hood, manufacturer installation guides typically allow 9 to 15m total equivalent run length depending on model, longer than 110x54 because the larger cross-section has lower pressure loss per metre. Each 90° bend adds around 1m equivalent length, each 45° bend around 0.5m. For MVHR installations, duct length is governed by the MVHR unit's external static pressure rating, so check the unit's commissioning data. Always minimise bends and keep the run as short as practical; excess length is the most common cause of fans and cooker hoods failing to hit their rated airflow.