Rectangular Duct is hung with 1″ wide 22 gauge (or 20, or 18 gauge) Galvanized Strips that is supplied to the field along with the fabricated ductwork.
10 ft strips, cut and bundled, is the most common. (Some shops use 100 lb coils though any savings in “drop” are negated by the much higher cost of the coiled strip)
Typically the field will put a hanger on every duct section (which means every 5 ft or 4 ft). One vertical strip on either side of the duct.
What Gauge to use?
With spacing every 5 ft, 1″ 22 gauge strap is SMACNA approved all the way to duct that is 144″ in total perimeter (adding up all four dimensions 144″ or smaller) and 20 ga is approved on duct with total perimeter of 192″. Shops that use 18 gauge might be doing so for one of three reasons:
- It’s what they “have always done”
- To cover all of their bases on even the largest duct
- Because they hang every other section of duct which means the spacing is every 8 ft or 10 ft
The Gauge of Hanger Strap that a shop uses therefore depends on the spacing that the field uses to hang the duct, the size of the rectangular duct and also whatever the shop standards are (whatever has been passed down over the years).
Whether to Cut in House or “Buy Out”?
Many Shops cut their own Hanger Strap in house using 5 x 10 (or 4 x 10) flat sheets in the shop’s 10 Ft Power Shear.
The shop will typically cut 1″ along the width of the sheet 48 or 60 times for that many pieces of 10 ft strips and they will do this on multiple sheets and then bundle 25 pieces at a time with duct tape near each end. If a shop is cutting their own Hanger Strap there are questions we ask them to determine whether they would find more value in “Buying Out” as 10 ft already cut and bundled.
A. Do you account for the cutting and bundling when you figure cost of doing in house? (do you figure the cost per foot of hanger strap based on the cost of the 5 x 10 sheet divided by 600?)
B. Are you cutting the straps from prime sheets? (unless the shop has white rust sheets to use up, there’s really not any drop that comes from a 10 ft sheet)
C. Is bundling the worst part? (it’s typically the bundling and not the cutting that’s the hassle)
D. Is labor becoming an issue? (finding good help in the shop seems to be a challenge in many areas)
E. Do you have to flip or sharpen the blade on your shear occasionally?
If you answer “No” to A and Yes to B, C, D and E, then consider moving away from this:
And try buying out your Hanger Strap in strips, already cut and bundled.
