This performance standard test protocol requires that the professional dryer exhaust duct cleaning contractor has thoroughly agitated the entire dryer exhaust duct system to dislodge accumulated lint from the duct prior to applying this test. This performance standard is the method of validating airflow combined with back pressure after the service has been completed.
A clean, unobstructed dryer exhaust duct system improves operating efficiency of the dryer appliance. As the dryer duct becomes obstructed with collected lint, drying time increases and the dryer can overheat, increasing energy consumption. In extreme cases, a blocked dryer exhaust duct or termination device can result in a fire within the dryer appliance or within the dryer exhaust duct system.
There exists a wide range of air velocity and pressure differentials between older model and new, high efficiency, internally-powered fan devices. New generation dryers use high blower strengths. Too many variables exist to support a single performance test using the internally-powered fan of the dryer appliance itself. Therefore, due to the wide variety of blower strengths affecting the duct velocity and back pressure, a new method was developed to consistently test dryer exhaust ducts. In order to compensate for these in field variations, the committee developed a new device and protocol that provides a reliable, consistent measuring methodology across all dryer exhaust ducts regardless of the dryer type or the power of the internal fan device. The development of this device and procedure was only possible because virtually all residential type dryer vents are 4″ in diameter.
I went shopping at a few retailers for dryer transition ducts, and I was quite surprised to learn that the material I've always recommended is not a UL listed product! If there are any manufacturers that do make a UL listed semi-rigid duct, they've done a good job of hiding their products - even online.
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