Because of important safety and efficiency issues, building code and appliance manufacturers outline very specific requirements for connecting the dryer to in-wall exhaust systems. In every instance the UL 2158A Standard provides core guidance. What is 2158A? Underwriters Laboratories has published extensive documentation for what is described as the Standard for Clothes Dryer Transition Duct. Under these guidelines, only transition duct that is Listed under UL 2158A should be used to vent clothes dryers.
To obtain this listing, transition duct must meet very specific construction requirements and successfully pass performance tests that include surface burning, flame resistance, bending, corrosion resistance, puncture, impact and tension tests.
ICC publications for residential and mechanical building code both include extensive clothes dryer exhaust requirements to address efficiency and safety issues. The full text of sections IRC M1502 and IMC 504 cover all details of the dryer exhaust system including installation, duct run-length and materials required. Specifically for dryer duct, M1502.4.3 and 504.6.3 state:
UL2158A Class 1 versus Class 0 Materials The old collquialism—Looks can be deceiving—applies to UL2158A listings and the various transition ducts available. Walking through the dryer venting section in a bog box store, you'll see a variety of options including white vinyl flex, "slinky foil" duct, semi-rigid aluminum, and rigid pipe. Few of these options carry the UL2158A listing and still, the UL listed products may not be sufficient to meet building code requirements and / or appliance manufacturer's specifications.UL2158A is broken down into two categories: Class 1 and Class 0.