8″ 90° Duct Elbow (Compact)

Description

90 degree duct elbow, 8 inch, compact envelope

A 90 degree duct elbow in 8 inch is what you fit when the building has already decided the route. Joists run where they run. The wall cavity is the width it is. The trunk has to drop vertically the moment it clears the machine, and there is no negotiating with any of it. This elbow takes that right angle inside 249.2 × 249.2 × 210.4 mm, about as tight as an 8-inch turn can be drawn while keeping the bore fully open.

Standard 8-inch collars on both ends, mating every 8-inch shroud, silencer, coupler, wye and port in the line. Printed as one continuous body, so there is no glued seam in the part of the run that works hardest.

Where the layout gives you length instead of a corner, the 8″ 45° elbow and the 8-Inch Long-Radius 90° Airflow Duct Elbow are the fittings for it.

What it fits

Standard 8-inch duct on both ends, rigid or flexible. It is the right part for wall drops, joist clearances, rack backs, and any turn where the envelope is fixed by structure rather than by choice. It is the wrong part for a long trunk with room to spare, where two 45s or a long-radius sweep will serve you better. On 6-inch runs, the equivalent is the 6″ 90° Duct Elbow (Compact).

How it is used

Fit it to the fixed end first — the shroud, the wall sleeve, whichever side you will not be able to reach afterwards — clock it to the outgoing direction, and clamp. Then bring the run onto the second collar and clamp that. Because the part carries real weight in 8-inch, strap the duct on both sides within about half a metre so the elbow is sealing the joint rather than hanging from it.

If the run also has to change size near the corner, turn first and reduce second with the 8″ to 6″ reducer. Reducing before the bend means the turn happens in the smaller, more restrictive cross-section, which is the more expensive order to do it in.

Why the compact envelope is the point

Eight-inch duct is big, and a right angle in it is bigger still. The alternative to a fitting that fits the bay is a run that gets forced — flex duct crushed against a joist, an elbow tilted so the collars load their clamps sideways, a trunk kinked to squeeze past a stud. Every one of those is a worse restriction than the bend itself, and every one of them leaks. Keeping the turn inside a known envelope keeps the rest of the run round, straight and sealed.

• Takes a full right angle in 8-inch inside a 249.2 mm envelope
• Clears joist bays and wall cavities without crushing the duct either side
• Holds the bore open through the turn rather than flattening it
• Clocks to any orientation before the clamps go on
• Mates the full 8-inch line, including the wye trunk and window port

Specifications

Open source — the geometry is ours and it is published

D-Central Technologies designed this elbow, drew every millimetre of its envelope, and released the file open source under CC BY-SA 4.0 at the 3D models download center: download it, modify it, remix it, print it, sell what you print. Its own card is the compact 8″ 90° elbow model. An 8-inch 90 is a demanding thing to make well at home, which is precisely why the drawing should be free even if the part is not.

The file is elbow_90_8.zip — STL, CC BY-SA 4.0 licence, installation and safety guide. What this page sells is the finished elbow: made to order in PETG in black or orange, shipped from Montreal, Quebec, cut to the same collar standard as the rest of your run. The download stays free regardless; buying the part, or backing D-Central’s fund page, is what puts the next drawing on the board.

Works with

• 8″ 45° Duct Elbow
• 8-Inch Long-Radius 90° Airflow Duct Elbow
• 8″ Duct Coupler
• 8″ to 6″ Duct Reducer
• 8″ Window Exhaust Port

The full chain from shroud to wall, one collar standard throughout: see the D-Central shroud and ducting system.

Frequently asked questions