Radial Ducting

About

Radial ducting is the standard distribution method for modern whole-house Mechanical Ventilation with Heat Recovery (MVHR) and Mechanical Extract Ventilation (MEV) systems. Rather than branching a single large duct progressively smaller as it serves each room, a radial layout runs an individual semi-rigid duct from a central manifold direct to every supply and extract point. Each room effectively gets its own dedicated airway back to the unit. This has real practical advantages over traditional branch ducting. Because every run terminates at the manifold rather than crossing paths with other ducts, there's no cross-talk between rooms — no need for bulky acoustic attenuators at each valve to stop sound travelling duct-to-duct. The smaller duct diameter (typically 75mm or 90mm) fits far more easily through joists and ceiling voids than rigid steel branch ductwork, and the smooth-bore semi-rigid construction bends gradually around obstructions without extra fittings, keeping air resistance — and the associated fan energy penalty — low. Installation is typically faster too, since duct runs are pushed together with push-fit or push-click-lock connections rather than sealant and tape, and balancing airflow at commissioning is more straightforward with a manifold-based layout. Specifying radial ducting: things to get right Duct diameter vs. airflow. 75mm is standard for most residential extract/supply points; 90mm reduces air velocity further, cutting noise and running cost, but needs more ceiling void depth — check clearance before committing to size. Manifold placement and capacity. Manifolds are sized by number of ports; confirm the manifold matches both the room count and the MVHR unit's total airflow, not just the port count. Run length and bends. Semi-rigid duct tolerates gradual bends without extra fittings, but total run length and bend count both add resistance — long runs to distant rooms may need a duct diameter step-up. Fire stopping. Where ducts pass through c