Install guide
TDC duct connections
Get the duct aligned and controlled before you commit the connection. Do not fasten it together and then try to force the run into place.
Field-reviewedRectangular ductInstall sequenceUpdated July 2026
Field sequence
- Confirm the duct sizes, orientation, elevation, and fitting direction before bringing the sections together.
- Make sure the gasket is on one end of the duct. On the joining duct, place gasket at the corners as required by the job standard.
- Bring the duct sections close and match the duct itself for level and alignment. The corners do not have to look perfect yet; the duct bodies do need to line up.
- Use drift pins through the corner holes to pull the flanges into alignment. Drift before the connection is fully fastened.
- Clamp the connection so it stays seated and aligned while you work.
- Install the corners and cleats in the approved sequence. Do not rely on the corners alone to pull a badly aligned run together.
- When cleats are unavailable, 5/16-inch self-tappers through the flange may be used only as the field-approved fallback.
- Walk the full connection: gasket captured, flange seated, cleats secure, duct level, no twist, no open corner, no sharp edge left exposed.
Stop and get direction when
The duct sizes do not match, the flange is damaged, alignment requires crushing or distorting the duct, the connection conflicts with structure or another trade, or the approved fastening/sealing method is unclear.
Say this
“I’m at [location]. The duct is matched for level, but the TDC corners will not seat cleanly. I drifted and clamped it before fastening. Can you check whether the flange is damaged or you want a different connection method?”
Before you leave it
- Duct bodies match in level and alignment.
- Gasket is continuous and captured.
- Corners and cleats are installed and seated.
- Connection is not twisted or forced.
- Seal and fastening match the job requirement.