airtightness class A, B, C and D (of a duct)
[EN 12792:2003, 35]:measure of the tightness of a ductwork system, defined at the upper limit of the air leakage factor f(see also leakage)
[EN 12792:2003, 35]:measure of the tightness of a ductwork system, defined at the upper limit of the air leakage factor f(see also leakage)