Ductwork airtightness can be defined as the resistance to inward or outward air leakage through the ductwork shell. The limit values for the maximum air leakage volume flow in duct systems are defined in the 4 tightness classes A to D which is now transformed into 7 new Air Tightness Classes ATC 1 – ATC 7  in different European standards, e.g. EN 12599, EN 16798-3, EN12237or EN1507.

See also

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