Duct cleaning brushes: the right brush and shaft

Why does a rotating brush work so well in air ducts?

Dust does not just lie loose in a duct. The US EPA points out that a lot of dust stays stuck to the wall. A rotating brush loosens it mechanically, while an extraction unit removes the loosened dust under negative pressure. That is the classic combination used by cleaning contractors, alongside compressed air, robots with cameras and manual work.

The big advantage of a brush is force on the wall. With larger cross sections and dirt that is stuck, a spinning brush removes more than air alone. The drawback: a brush starts at a certain minimum size. For very thin ducts, compressed air duct cleaning is often the better choice.

Which duct brush do you choose: soft, standard or Tynex?

You match the stiffness of the brush to the duct material and the type of dirt. Danduct Clean supplies three types.

Source: Danduct Clean, shaft brushes, and the US EPA, checked on 6 October 2026. The EPA recommends soft brushes for fibreglass duct board and for sheet steel. So when in doubt, start soft and only step up if the dirt will not come loose.

For the Danduct Clean DC4 duct cleaner, Lamers lists polypropylene brushes with bristles of 0.6 and 0.9 mm. The larger package contains an aggressive set of seven pieces in addition to the standard brush set.

How do you determine the right size of ventilation duct brush?

The brush must touch the wall all round. If it is too small, it spins through the middle and the dust stays on the wall. If it is too large, it runs heavily and can get stuck in a bend. This is how to approach it:

1. Measure the internal size. For round ducts the diameter, for rectangular ducts the width and height.
2. Look for reducers. A run that goes from large to small requires several brushes or several passes.
3. Choose the set. The DC4 brush sets consist of seven brushes from 100 to 600 mm, so you can change per run.
4. Test on a straight section. Check that the brush makes even contact before you go into a bend.

If you work with rectangular ducts, Lamers states that the DC4 can handle both round and square ducts. Discuss the ratio between width and height with Lamers, because a round brush in a flat duct does not reach everywhere.

Which shaft goes with your air duct brush?

The shaft carries the brush to the dirt and keeps it on course. The length determines how far you can get from an opening, the stiffness how well you get through bends.

Source: Lamers and Danduct Clean, checked on 6 October 2026. Danduct mentions soft shafts for small ducts with bends. On the DC4, a light solid steel shaft keeps the brush in the centre of the duct, which helps it touch the wall evenly. For short sections, the compact PD4 duct cleaner is a handy option. For the specifications of the PD2 from Lamers, ask Lamers.

Also important: the distance between openings. A Eurovent recommendation mentions inspection openings no more than 10 metres apart, or after no more than two bends of 45 degrees or more. Ducts larger than 500 mm need an access panel of at least 500 by 400 mm.

How do you take a duct brush through bends and vertical sections?

Bends are where dust accumulates and where brushes get stuck. According to Lamers, the DC4 is designed for vertical ducts and 90 degree bends. A few practical tips:

• Let the machine do the work and do not push hard through a bend. A shaft that kinks loses contact with the wall.
• Use the automatic left to right system of the DC4, which you set on a timer. Ask Lamers which setting suits your run.
• Adjust the speed. The DC4 has adjustable speed: lower in bends, higher on straight sections.
• On vertical sections, work from top to bottom where possible, so that loose dirt falls towards the extraction.

If you come across bends that are too tight for a brush, a compressed air nozzle with a camera is a useful addition. See also the overview of tools for cleaning air ducts.

Brushing alone or with a spray system and extraction?

According to a Eurovent recommendation, dry brushing is usually sufficient for supply ducts and general extract ducts. Extract ducts from commercial kitchens require wet methods, because grease does not come loose like dust. A spray system exists for the DC4, the DC4 Sprayer System. What exactly you can do with it is something to discuss with Lamers.

With greasy kitchen extraction the insurer also plays a role. An insurer such as Goudse requires fixed, non flexible and non corrugated ductwork of aluminium or steel in hospitality. More on this on the page about removing grease from kitchen extraction.

Either way: without extraction, brushed off dust goes into the room or the system. The EPA mentions exhausting through a HEPA filter or to the outside. How to set that up is explained under duct sealing and extraction.

Common mistakes when choosing an air duct brush

Starting too hard. A Tynex brush on duct board or a thin walled duct can damage the inside. Start soft.

One size for everything. Buildings have reducers. With a set of seven sizes you can change per run.

No check afterwards. A brush without a camera does not show what is left behind. Combine it with inspection, especially at bends.

Brushing without a plan. Know beforehand which runs you will do and in what order. A step by step plan helps: see the duct cleaning method.

Fictional example: a facilities team uses one large brush for a run that narrows from 400 to 200 mm. The wide section gets clean, the narrow section does not, and the brush gets stuck in the reducer. With two sizes and an opening at the reducer, it would have gone right the first time.

Quick checklist before you start brushing

• Internal size of every run measured and noted.
• Duct material known, so the stiffness matches the wall.
• Shaft length checked against the distance between openings.
• Extraction connected and the section under negative pressure.
• Camera or inspection planned for bends and reducers.