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Frequently Asked Questions
How does square duct differ from rectangular?
Practically rather than fundamentally.
A square section is symmetrical.
One band size covers the section in either orientation.
Installation is marginally simpler.
The support principles are identical.
Load still has to be spread across the section rather than concentrated.
What sets the support spacing?
Ductwork standards, by size and construction.
The intervals exist because unsupported duct sags.
Sagging duct opens its joints and leaks.
A leaking system moves less air for the same fan energy.
Leakage is frequently a tested and specified requirement.
The hanger manufacturer does not set the spacing.
Where should the load bear?
Under the duct, through a bearer, rather than on its sides or corners.
Thin sheet deforms where load concentrates.
Corners in particular should not carry weight.
Two hangers per point carrying a bearer is the usual arrangement.
That puts weight into the duct's base.
It is what the sheet can actually take.
Does insulation change the support?
It is the same trap as on any insulated duct.
A band tightened over insulation crushes it.
That produces a thermal bridge at every support.
On cold duct it causes condensation where the metal is coldest.
Load-bearing inserts carry weight through the insulation.
Supports outside the insulation achieve the same thing differently.
What weight should be allowed?
Duct, insulation, lining and years of accumulated debris.
Empty duct weight is a poor guide to what supports carry after a decade.
Systems collect dust throughout their life.
Lining adds weight along the whole run.
Insulation adds both weight and bulk.
Calculating loaded weight avoids supports adequate only when new.
Does support position affect cleaning?
It can, and it is easier to solve at installation.
Ductwork requires periodic cleaning in many building types.
Access panels have to be reachable.
A support across an access panel makes the regime harder.
Coordinating support positions with access panels is straightforward at design stage.
Moving a support afterwards means disturbing a live system.
Do the same code requirements apply?
Yes - seismic bracing and fire strategy provisions both.
Wire suspension resists gravity rather than sway.
Bracing is a separate provision where seismic rules apply.
Services in a fire strategy may need certified supports.
Requirements differ substantially between markets.
The local code governs alongside the ductwork specification.