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Duct system air leakage - How Scandinavia tackled the problem

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This paper describes the Scandinavian approach concerning the tightness of air ductwork in buildings. It gives recommendations on how such successful approach can be adopted in other countries.
Duct leakage is detrimental to indoor air quality (IAQ), comfort, and energy efficiency. It is often accompanied by other problems, such as inferior commissioning and cleaning. Airtight circular (round) ductwork is known to have many other benefits over rectangular ductwork, including cost. But why do designers, installers, and building owners forego airtight duct systems- It is due to: (i) lack of awareness of the benefits, (ii) lack of performance requirements and penalties for noncompliance, and (iii) no one is found accountable, as there is no commissioning.
Conversely, in Scandinavia, high-quality airtight systems are the norm. 90~95% of ductwork in Scandinavia is now circular steel ductwork with factory-fitted airtight gasket joints (Class C or better). Sweden has spearheaded this development. This impressive result has come about after the problem of leakage was first identified in the 1950s, leading to the first contractual requirements on ductwork airtightness in the 1960s (e.g. Swedish VVS AMA). Since then, the requirements have been tightened concurrently with advances in duct technology. There is strict  control in Sweden, Finland and Denmark, so most installations comply with these stringent requirements after commissioning.
This paper focuses on metal ductwork, but mentions other materials.