When a Duct Shop sends out Rectangular Ductwork to the jobsite, they also send out the Hanger Strap required to hang the duct. Most Rectangular Duct under 32” (on the two horizontal sides) is hung by means of 1” Flat Hanger Strap. On straight duct runs every 4 ft or 5 ft along the Duct, a strip of Hanger Strap approx 4 to 5 ft extends from the ceiling to either side of the duct where it’s then bent to a 90 degree angle and attached to the bottom edge of each side of the duct by means of a screw.

The spacing will vary some according to the duct dimensions and when there are fittings like Elbows and Offsets. Contractors will vary on the gauge and sometimes the width of this flat hanger strap but 1” 22 and 20 gauge will, at 5 ft spacing, cover almost all of the jobs hung with Strap according to SMACNA’s chart.

The allowable load of each gauge is figured using 1″ wide strap: 22 Gauge will support 260-lbs, 20 Gauge will support 320 lbs, 18 Gauge will support 420 lbs.

For larger duct—or when specified by the engineer—Threaded Rod coming down from the ceiling and used with Strut as a Trapeze Hanger are used instead of Hanger Strap.