Most of the METU-SYSTEM profiles are also available with injected sealant (hd). The profile choice according to the air-tightness requirements is therefore independent from the profile choice based on stability requirements. When using hd profiles leakage is practically eliminated, thus allowing the total ductwork leakage to be reduced by 30% to 50% at very little additional cost.

Recommendations for the Ductwork Manufacture According to DIN EN 1507

Class A (ATC 5, EN 16798-3)

Flanges can be made with METU-SYSTEM profiles without injected sealant. The corner area of the flange however has to be carried out with care.

Seams should also be folded precisely if no additional sealant is to be applied.

During assembly extra care should be brought to properly cover the exposed edge of the duct in the corner area with gasket.


Class B (ATC 4, EN 16798-3)

Flanges should be made with METU-SYSTEM profiles with injected sealant (with “hd”). The corner pieces have to be sealed with mastic.

The seams on ducts with duct edges above 500 mm have to be of high quality. We recommend to apply mastic on snap lock seams. The seams on ducts with duct edges below 500 mm should also be all sealed with mastic, as their number per m2 of duct is larger. The easiest way to do this is to apply the mastic inside the ducts right after their manufacture.

During assembly we recommend applying two layers of gasket in the corner piece areas. This is especially important if you use S type corner pieces.


Class C (ATC 3, EN 16798-3)

Flanges have to be made with METU-SYSTEM profiles with injected sealant (with “hd”). After installing the flange onto the duct, the corner area has to be sealed with mastic.

All seams have to be sealed carefully with mastic. The easiest way to do this is to apply the mastic inside the ducts right after their manufacture. 

Two gasket layers and/or mastic should be applied in the corner piece area. You should make sure that the gasket layers are placed adequately on the exposed edge of the duct which is not covered by the profile.

Class D (ATC 2, EN 16798-3)

This air-tightness class can only be achieved through proper workmanship and careful installation practices.

In addition to the caulking measures required for the air-tightness class C, a mastic sealant can be applied along the entire length of the flange without requiring an hd profile version. In this regard, we strongly suggest that you conduct your own air-tightness tests, as this is the only way to determine precisely which sealing measures are sufficient. This is especially important if the installation is done by a third party.

The assembly must be carried out with the greatest care. Mastic sealants (applied on the face of the profiles) usually bring better results than the more common self-adhesive foam gaskets bands. Special caution is necessary in the corner piece areas. Also very important is to select large and sturdy enough profiles and corners in order to guarantee that enough compression is exerted on the gaskets and/or mastic at all points of the connection.

For all duct work designed for operating pressures above 1000 Pa, METU-SYSTEM hd profiles should be used.

For higher tightness requirements (i.e. class D and above, ATC 1, aerosolate or oil-tight ducts) we recomment the METU-FORM system of ducts, fittings and connections.


Important Notice: 
The recommendations above are based upon our 30 years experience in duct work manufacturing (prior to 1987). However, no liability is accepted for the information provided above. Please keep in mind that leakage is the sum of many smaller leaks. In order to achieve the requirements it is therefore important to respect all the relevant points described above. A bad installation can make an airtight ductwork leak, but a very careful installation cannot make bad ductwork airtight!