Stiffening bead requirements only pertain to materials with pressure ratings up to 3″ W.G. and a thickness of 20 gauge or less. The majority of our double wall fittings — like Square Throat Elbow Ducts — are constructed using Pittsburgh seams. Additionally, our double wall fittings come fully assembled and complete with necessary accessories including TDC corners, vanes and rails.
The Rectangular Doublewall Square Throat Elbow is constructed with TDC end treatments. There are two different types of applications:
• Acoustical double wall duct for noise control
• Thermal double wall duct for temperature control