Spiral & Round Duct · Straight Runs & Assembly
Spiral concentric reducer
Centered size change
ConnectionSlip-fit/gasketed reducer
SupportSupports on adjacent straight sections
Before you start
- Reducers are directional.
- Confirm the airflow direction before you lift it.
- Confirm the reduction is what the drawing calls for; an abrupt reduction that the design did not intend is a pressure loss and a noise complaint.
- Stage the needed tools and materials before lifting the section: Reducer, supports for the adjacent straights, sealant or gaskets, fasteners, level, tape..
Tools and materials
Reducer, supports for the adjacent straights, sealant or gaskets, fasteners, level, tape.
Lay it out
- Confirm airflow direction and orient the reducer correctly. Mark it on the fitting so nobody flips it while you are on the ladder.
- Align the centerlines. On a concentric reducer both ends share a centerline and if they do not, one of your straights is off.
Set and support it
- Support the larger side and the downstream run. The reducer sits between supported pipe; it is not a hanger point.
- Use the approved support method for this condition: Supports on adjacent straight sections.
Make the connection
- 1
Fully seat the large end.
- 2
Fully seat the small end.
- 3
Seal and fasten evenly around both joints.
Check the install
- Centerlines aligned; sight through it.
- No denting from forcing the fit.
- Orientation correct for airflow.
- Both joints concentric and fully seated.
Common mistakes
- Hanging a support off the reducer. It is a transition fitting, not structure.
- Reducer in backward. It happens more than anyone admits.
- Stretching a reducer to cover a gap because the pipe came up short. Cut a new piece.
- Centerlines off, so the downstream run steps sideways.
Stop and ask
Stop if reduction is too abrupt for project design or reducer is being stretched to cover a gap