23 October 2017

An introduction to ductwork


Ductwork is tubing through which air or waste gases are blown in heating, ventilation or exhaust systems. The tubing is frequently a metal pipe, but can be any material and have any cross-section.

An introduction to ductwork

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Whilst often essential in factories to remove dust and fumes, equipping offices and domestic homes with ducts can provide effective heating and air-conditioning solutions, allowing connection to heat exchangers or easily routing warm or cool air to wherever it is most needed. With appropriate filters it is an effective means of removing allergens that cause asthma and hay-fever.

Flow control

A ductwork blast gate damper is a simple device to control the airflow in ducts. It usually consists of a simple plate assembly with brackets to connect the ducts – on one or both sides – and a sliding gate that can be lowered or extracted to regulate the passage of air.

Butterfly dampers and multi-leaf dampers are also often casually called blast gates but have slightly more elaborate ways of opening and closing the valve. In a butterfly gate, the damping plate is rotated between horizontal and vertical inside a tubular bracket; in a multi-leaf gate, several plates rotate somewhat like a venetian blind.

An introduction to ductwork2

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Circular cross-section ducts are most common; however, each type can as easily be rectangular, which makes sense in a rectangular space to optimise the flow capacity.

When flow pressure is high, the sliding type of ductwork blast gate damper from a stockist such as https://www.dustspares.co.uk/Blast-Gate-Damper.html provides a more rugged solution: the damping plate secured into grooves inside the damping bracket.


Qualified service technicians use instruments to measure air-flow and air-quality, giving early warning of developing problems.

In large air-conditioned buildings, one concern in the past has been legionnaire’s disease. This problem was caused mostly by attached air cleaning units, but such infections can easily spread through unserviced HVAC ductwork.

Dust, fluff or grease inside ducts can become a fire hazard, especially in kitchen extractors and heating systems. Even if it does not ignite, slow scorching can generate an unpleasant smell in air-conditioned buildings with poorly maintained ducts.

Blockages in ducts that carry carbon monoxide are obviously serious hazards. Damaged ductwork accessible from outside has been known to become home to unwanted guests, with bird nests and dead possums doing little to help systems work reliably.