duct fasteners

Mastic doesn’t hold ducts together, although the designation duct mastic suggests adhesive properties. To secure duct connections and sections, you need screws, staples and draw bands…

Securing insulation to the ducts

Ducts should be well supported to avoid joints to be pulled apart or damaged. But it is not just the ducts that need to be secured with mechanical fasteners. The insulation materials used in duct insulation also require to be secured.

In this case you may use pressure-sensitive tapes and draw-bands, rust resistant wire, staples or even nails.

Pressure-sensitive tape is mostly used in faced insulation materials. The tape should be wrapped several times (3 at least) around the duct.

Draw bands and multiple-staggered wraps of tape are largely used to secure the overlap of the insulation material in joints.

Other fasteners are mainly used with unfaced materials, and applied along the whole length of the insulation, every 15-20 inches.

Screws

Screws are the main mechanical fastener to secure duct connections and sections.

They are largely used in round sheet metal ducts using sleeves and fittings, to ensure that the joints don’t become separated. In this case, install some screws (3 or 4, at least) equally spaced around the joint.

Duct sealing and fastening Images credit: DOE

For vertical connections using flexible duct, screws should be installed conjointly with the draw-band, to prevent slippage: see image above.

When securing duct boots, also use screws. Duct boots should not rely on the ducts for support.

Draw-bands

Draw-bands are used to join two flexible ducts or to join one flexible duct section to other type of duct. In this case, the flexible duct is fitted over a collar and attached with two draw-bands: the first to secure the inner lining and the second to attach the outer insulation jacket.

Staples and Tape

Fiberglass duct boards can be fastened using embracing staples. If the use of staples isn’t feasible, exceptionally, use pressure-sensitive tapes.