Proven Solution for Sealing Industrial Ductwork: Covalence TWDB

 

If you work with industrial HVAC and piping systems, chances are you’ve come across Covalence (formerly Raychem) TWDB. TWDB is a thermofit, wrap-around duct band specifically designed to create a pressure-tight seal on ductwork—helping ensure long-term system integrity even in challenging environments.

Engineered for reliability, TWDB delivers a durable seal that stands up to demanding conditions where traditional sealing methods often fall short. Once installed, it provides confidence that your ductwork will remain protected and leak-free over the long haul.

For ease of use in the field, TWDB is stocked in both 3" and 4" widths and supplied in a 165-foot continuous roll. Each roll is packaged in a purpose-built box that allows installers to quickly and accurately measure the required length before cutting, reducing waste and improving installation efficiency.

Installation is straightforward and familiar to most crews. TWDB can be applied using either a propane torch or an industrial heat gun, allowing it to conform tightly to the duct surface and activate the thermofit properties that make the seal so effective.

TWDB is not a new or unproven product—it has seen consistent use for decades across industrial applications. That longevity speaks to its performance, reliability, and the trust it has earned among contractors and maintenance professionals alike.

When long-term sealing performance matters, Covalence TWDB remains a simple, proven solution.

Duct Band Heat Shrink

Heat Shrink for Duct Bands

     Thermofit Wraparound Duct Bands (TWDB) is Raychem's (now called Covalence) product fpr solving the problem of costly joint leaks in air conditioning duct systems.

     This duct sealing band, made of cross linked polyolefin heat shrinkable material, is precoated with a hot melt adhesive.  When heated in excess of 250F, TWDB shrinks and the adhesive melts, forcing it into all surface irregularities.  Mechanically strong, pressure tight seals are provided. 

     Ducts can be assembled on the floor and raised into position shortly after installation.  TWDB's cut to length system keeps inventory cost minimal by eliminating the need for multiple sizes.  Its wrap around design makes it suitable for flat oval and rectangular duct as well. 

     Used in high velocity systems operating up to 158F, TWDB is non toxic and resistant to solvents and vibration.  Shelf life is unlimited.  This product offers an efficient, neat and permanent method for sealing duct joints, all at a low installed cost. 

     As you see here, the installation procedure is quite simple. 
1:  Cut TWDB to appropriate length.  Recommended overlap is 2 inches onto itself.
2:  Using a heat resistant tape (supplied) secure the TWDB end by taping it in place to form the TWDB into a circle (or rectangle).
3:  Using a standard propane torch, heat TWDB on all sides until it has shrunk uniformly and adhesive is showing at each end.  

Thermofit Wraparound Heat Shrink Duct Bands (TWDB*) Installation Guide

Thermofit Wraparound Heat Shrink Duct Bands (TWDB*) Installation Instructions

TWDB is heat-shrinkable tape for sealing duct joints on round air conditioning or heating systems.

Materials and Equipment Needed for Install:

1. Raychem TWDB (supplied with high temperature closure tape)
2. Raychem torch (or equivalent)
3. Propane gas tank, regulator and hose
4. Gloves

Recommended TWDB tape widths:

Duct to Fitting to 24" -2” width
Duct to Fitting > 24" -3” width
Duct to Duct ³ 12” -2” width
Duct to Duct 14-48” -3” width
Duct to Duct > 48” -4” width

1. Join duct sections using internal couplers or crimped end male/female type connection. Apply sheet metal screws. 2 screws 180° apart are usually sufficient.

2. Wipe joint area to remove foreign materials. Preheat joint to remove moisture and burn off surface oil that may be present.

3. Cut TWDB to appropriate length. See sizing chart on reverse side. Center TWDB and wrap around duct joint.

4. Using the Tyco Adhesives supplied high temperature tape, secure the loose TWDB end by taping in place.

5. Using a standard propane torch, heat TWDB on all sides until it has shrunk uniformly and adhesive is showing at each end.

6. Smooth down the overlap area with gloved hand to ensure proper contact to duct.
Note: See below for rectangular and flat oval duct.

                                                                                                                                                                      

TWDB may be used to seal
rectangular ducting. The proper
length to cut is shown below.

Length of TWDB
=2 + Perimeter
=2 + 2 (L+W)
Dimensions in inches.
Note: Be sure to measure outer
dimensions as size on print often
refers to internal dimensions.

TWDB may be used to seal flat
oval ducting. The proper length
to cut is shown below.

Length of TWDB
=2 + Circumference
=2 +2.2 Square root of A2 + B2
Dimensions in inches.
Note: Be sure to measure outer
dimensions as size on print often
refers to internal dimensions.

*Install TWDB on rectangular and flat oval duct following the procedures for round duct with the following additional step: Immediately after shrinking is complete, press down the still hot TWDB with roller or gloved and on flat sections.