100mm Round PVC Ducting Pipe

100mm round PVC ducting pipe — also called 4 inch ducting, 100mm plastic pipe, 100mm round ducting, or Domus EasiPipe System 100 — is rigid round PVC ductwork designed for 100mm extract fans, domestic cooker hoods, bathroom and toilet extract, tumble dryer extract, and MVHR supply or extract runs. It's the direct round alternative to 110x54 flat rectangular ducting: same airflow capacity, lower pressure loss per metre, cheaper parts, and specified wherever the installer has the depth to run a round duct.

We stock the full Domus EasiPipe range in 100mm: 2m, 1m and 350mm straight lengths, 90° right-angle bends, 45° bends, T-pieces, Y-pieces, straight connectors, spigot adaptors to step up (100mm to 125mm, 100mm to 150mm) or down (100mm to 80mm, 110mm to 100mm), threaded hose connectors, and flexible EasiPipe hose in 15m and 45m coils for longer or awkward routes. All parts are push-fit with gasketed sockets for an airtight joint. In stock with next-day UK delivery. 

All Round PVC Ducting / 125mm Round / 150mm Round / 110x54 Flat Equivalent

What is 100mm round ducting?

100mm round ducting is rigid circular PVC ductwork with a 100mm internal diameter — the standard UK size for domestic extract. It's sometimes called 4 inch ducting (100mm is the metric equivalent of the imperial 4 inch size), and in the Domus system it's branded EasiPipe System 100. The 100mm diameter is matched to the spigot size on the vast majority of domestic extract fans, bathroom fans, toilet extract fans, standard cooker hoods, and through-wall extract kits sold in the UK. A 100mm round duct has a slightly larger cross-sectional area than 110x54 flat, so pressure loss per metre is marginally lower — worth specifying round where the void depth allows it.

What is 100mm round ducting used for?

Bathroom, toilet and utility extract fans, standard domestic cooker hoods, tumble dryer extract, kitchen extract in older or smaller properties, through-wall and in-line extract applications, and MVHR supply or extract terminals. Almost every domestic 100mm extract fan on the UK market — Vent-Axia, Greenwood, Xpelair, Airflow, Domus itself — has a 100mm spigot designed to push directly into EasiPipe or flexible 100mm hose. For larger kitchen hoods (125mm spigot) step up to 125mm round or 204x60 flat; for MVHR trunks (150mm) step up to 150mm round or 220x90 flat.

Is 100mm round the same as 4 inch ducting?

Yes — 100mm is the metric name, 4 inch is the imperial name, and they refer to the same nominal duct size. UK ducting is manufactured in metric (100mm internal diameter) but older specifications, builders' merchants and some manufacturer catalogues still use the 4 inch label. Any "4 inch" branded extract fan, cooker hood or wall kit will fit standard 100mm round EasiPipe ducting. The same applies for 125mm/5 inch and 150mm/6 inch.

What's in the Domus EasiPipe 100mm range?

The full EasiPipe System 100 round range: 2m straight lengths (1200-4), 1m straights (1100-4, 2100-4), 350mm short straight (135-4) for tight sections, 90° right-angle bends (490), 45° bends (491), T-pieces (492) for branched runs, Y-pieces (499) for split runs, straight connectors (493) to join two ducts end-to-end, spigot adaptors stepping 100mm to 125mm (119), 100mm to 150mm (619), 110mm to 100mm (120) and 100mm to 80mm (DD019), threaded hose rounded connectors with spigot (124-4) for connecting flexible hose, and flexible EasiPipe hose in 15m coils (3615) and 45m coils (3645).

Should I use 100mm round or 110x54 flat ducting?

Airflow-equivalent, but the right choice depends on void depth. Use round 100mm where there's enough depth (100mm+) in the ceiling void, stud wall or chase — it's cheaper, has lower pressure loss, joints less often, and the Y-piece and T-piece range is richer. Use flat 110x54 where depth is restricted — typically above kitchen wall units, through shallow ceiling voids, or between close-spaced floor joists. Most domestic cooker hood installations use flat 110x54 behind the units because of the depth restriction. Most bathroom and utility extract uses round 100mm because there's more space to run round duct in a loft, airing cupboard or chase.

How do I connect 100mm EasiPipe to a flexible hose?

Push the flexible 100mm EasiPipe hose over a threaded hose rounded connector (Domus 124-4) or directly onto the spigot of a rigid EasiPipe part. Secure with a jubilee hose clip — a 125mm clip for 100mm flexible hose because the corrugated outer diameter is larger than the nominal 100mm bore. Apply a bead of duct sealant before clamping for airtight joints. Keep flexible sections short — ideally under 1m — because flexible hose has significantly higher pressure loss than rigid EasiPipe. Use rigid for the main run, flexible only for the final connection or to absorb misalignment.

How do I join 100mm EasiPipe sections?

EasiPipe uses push-fit joints with integral neoprene gaskets. Slide the plain end of one duct into the socketed end of the next, or use a straight connector (Domus 493) to join two plain ends. For airtight joints — essential on MVHR and Building Regs extract — apply duct sealant inside the socket before pushing home, then foil-tape over the joint externally. Fix horizontal runs every 600–800mm with duct clips to prevent sag and reduce noise transmission. Bends and T-pieces have sockets at each leg, so they simply push between duct sections.

What's the maximum run length for 100mm ducting?

For a standard 100mm extract fan, manufacturer installation guides typically allow 6–12m total equivalent run length depending on fan model — stronger fans (centrifugal, in-line) allow longer runs than axial wall fans. Each 90° bend adds approximately 1m equivalent length, each 45° bend approximately 0.5m. Keep runs as short as practical, minimise bends, and pull any flexible sections taut. Excess duct length is the most common cause of bathroom and utility fans failing to remove enough moisture. For runs longer than the fan's rating, specify a more powerful fan or consider stepping up to 125mm round for lower pressure loss.

Can I use 100mm round ducting outside?

Short external terminations are fine — most external wall kits and cowls are designed to connect to 100mm round. For longer external runs, consider aluminium or galvanised spiral instead of PVC, as prolonged UV exposure will eventually degrade PVC. Terminate with a proper cowl or external grille with integral backdraught shutter, never leave the duct end open. Insulate any external or cold-loft run to prevent condensation forming inside the duct where warm moist extract air meets the cold pipe wall.