Duct Support Calculator
Bracket count, steel weight, rod weight and anchors in one go.
Quick answer
With the default inputs: Duct length 30 · Bracket spacing 3 · Steel per bracket 1.4 etc.Total support steel 72.4 kg
Edit the inputs below to recalculate.Inputs
Result
Total support steel
72.4kg
| Bracket count | 11pcs |
| Total angle length | 15.4m |
| Angle steel weight | 60.96kg |
| Total rod length | 17.6m |
| Rod weight | 11.40kg |
| Anchors required | 22sets |
| Support steel per metre | 2.41kg/m |
Count uses spacing rounded down plus one end bracket — duct ends must be supported, so 30 m at 3 m gives 11, not 10. Code limits are 3 m horizontally and 4 m vertically, tightened to 2.5-3 m for insulated duct. Grilles, dampers, access doors, elbows, tees and transitions each need their own support; those are not included above and must be added from the layout drawing.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Bracket count | n = ⌊length ÷ spacing⌋ + 1 |
| Angle steel weight | W = n × steel per bracket × unit weight × (1 + waste) |
| Rod weight | W = n × rods per bracket × rod length × unit weight × (1 + waste) |
| Anchors | N = n × rods per bracket |
30 m of duct, 3 m spacing, 1.4 m of L50×5 per bracket and two 0.8 m φ10 rods at 5% waste: 11 brackets, 60.96 kg of angle, 11.40 kg of rod, 72.4 kg total, 22 anchors and 2.41 kg per metre.
How to work it out
- Bracket count n = ⌊total length ÷ spacing⌋ + 1. Spacing per code: 4 m maximum for horizontal ducts with a long side up to 400 mm, 3 m above that, and 4 m for vertical runs.
- Angle weight = n × steel length per bracket × unit weight × (1 + waste). Common values: L40×4 is 2.42 kg/m, L50×5 is 3.77, L63×6 is 5.72.
- Rod weight = n × rods per bracket × rod length × unit weight × (1 + waste). M8 round bar is 0.395 kg/m, M10 is 0.617, M12 is 0.888.
- Anchor count = n × rods per bracket, one anchor per rod.
- Total up and add 5-8% waste, then price by kilogram or tonne.
- Check the load while you are there: duct plus insulation plus flanges runs 15-20 kg per metre for a 1 m² section, so at 3 m spacing each bracket carries 45-60 kg — which sets the anchor size and the required concrete strength.
Where it goes wrong
- Computing length ÷ spacing without adding 1. A 30 m run at 3 m is ten spans and eleven brackets; counting ten leaves an end unsupported and the duct sags, opening the flanges.
- Using the wrong section weight. L50×5 is 3.77 kg/m against 2.42 for L40×4 — a 56% difference that halves or doubles the material plan.
- Forgetting the duct's own weight. The bracket carries duct, insulation and flanges, not just steel. Skipping this check means the anchors are undersized and a whole run can come down.
- Defaulting to 4 m spacing. Ducts with a 1000 mm long side are limited to 3 m by the code; at 4 m they sag visibly and vibrate at low frequency in operation.
Material and cost
Fabricated and installed supports run 8-15 CNY/kg including derusting and painting, or 15-25 CNY per proprietary bracket. Galvanised M10 anchors are 1.5-3 CNY each. Supports typically account for 8-12% of the ductwork package, and insulated ducts need anti-cold-bridge pads added.
On site
- Keep supports clear of grilles, dampers, access doors and control devices by at least 200 mm, or maintenance access is impossible later.
- On insulated ducts, fit anti-cold-bridge blocks or proprietary insulated saddles. Without them the support condenses and drips into the ceiling void, which gets reported as a leak.
- In risers, spacing may relax to 4 m but each vertical run needs at least two fixed supports to stop the whole length sliding down.
- The commonest estimating error is quoting in metres of section. Always convert angles and channels to weight — metres are not comparable across sections.
Basis
- GB 50243-2016 Code for acceptance of construction quality of ventilation and air conditioning works, supports and hangers
- 08K132 Standard drawing set, duct supports and hangers
- GB 50738-2011 Code for construction of ventilation and air conditioning works
FAQ
Why 11 brackets rather than 10?
Because both ends need support — one at the start, one at the finish, with spacing in between. 30 m divided by 3 m gives 10 spans, and 10 spans need 11 supports. This off-by-one is the most common take-off error in M&E; ordering 10 leaves you 10% short. The same spans-plus-one rule applies to pipe supports, cable tray brackets and purlins.
Can duct hangers be anchored straight into the slab?
Yes, subject to load and slab condition. A single duct bracket usually carries tens to a few hundred kilos, and M8-M10 expansion anchors into solid concrete are standard. But hollow-core slabs, precast planks, AAC walls, pour strips or cracked slabs must use through-bolts, chemical anchors or steel straps instead. Ducts over 2000 mm and plant-room supports need a proper load calculation.
Are seismic restraints mandatory?
For new schools, hospitals, malls and offices — densely occupied and key-defence buildings — seismic bracing of interior water, fire, HVAC and cable tray systems is mandatory under the code for seismic design of mechanical and electrical systems. Triggers are roughly pipe DN65 and above, duct section over 0.38 m², tray width over 400 mm. Bracing costs far more than ordinary supports, so omitting it from a quote is a serious loss.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Duct Support Calculator. 2026-10-25. https://jianzhujisuan.com/en/duct-support
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.