Dryer Exhaust Duct System (DEDP) Standard

dryer-exhaust-duct-system-performanceBelow is a general introduction into the new NADCA standard for measuring residential dryer exhaust duct performance. This standard was introduced at the NADCA’s 25th Annual Meeting in San Antonio recently.


This standard is for measuring residential single-dryer exhaust ducts for performance. It is a clothes dryer exhaust duct performance standard that is to be implemented directly after professional maintenance to determine if the dryer exhaust duct system meets minimum requirements for operation as specified by dryer manufacturers, national code requirements, and this standard.

Moisture and lint, byproducts of the clothes drying process, are transported by drawing ambient air from outside the dryer and channeling the air through electric or gas heating components. The air then passes through the dryer drum where moisture and lint enter the airstream. Air flows through the dryer’s lint filter to the internally-powered fan device and is discharged from the dryer appliance. At this point all airflow activity has occurred within the dryer appliance.

Next, the air exhausts the dryer through the dryer exhaust duct system, discharging to an exterior termination device. A typical exhaust duct system is comprised of a flexible transition duct behind the dryer, 4″ round (100 mm) rigid galvanized pipe, galvanized elbow fittings and a dryer exhaust duct termination device located outside the home.

Dryer Vent Cleaning


It is the purpose of this standard to define a measurable post-maintenance methodology for residential-type dryer exhaust ducts. This standard can also be applied when validating dryer exhaust duct performance in new residential construction installations.


This standard is designed to test the performance of a dryer exhaust duct system after servicing and to provide quantifiable testing method for performance validation. The dryer appliance is not included as part of this standard.


The standard establishes a repeatable, consistent criteria to evaluate the performance of dryer exhaust ducts after cleaning has been completed. These performance measurements and implementation protocols were developed primarily to validate a contractor’s work to the consumer and identify if other conditions potentially exist that may be affecting the dryer exhaust duct efficiency. This standard may apply to other materially interested parties (e.g., property owners and managers, insurance company representatives, government and regulatory bodies) when servicing residential-type dryer exhaust ducts. The performance protocol data for the dryer exhaust duct has been developed in accordance with dryer ducts installed according to local, state, and federal codes. (International Mechanical Code 2012)

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.


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.


This standard does not include an assessment of cleanliness within the dryer appliance. This NADCA standard does not specifically address any and all hazards or risks that could be encountered when performing work in accordance with this document. Instead, the user is directed to rely on the Authority Having Jurisdiction (AHJ), and the manufacturer’s guidelines.

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.

Manufacturers of dryer appliances have long specified that dryer exhaust duct systems must be serviced on a regular basis to remove accumulated deposits of lint. Several factors can contribute to accelerated lint accumulation or restrictions within the dryer exhaust duct system. These include extended ductwork lengths, restricted ducts, bird or rodent nests in the termination, crushed or kinked flexible transition duct, terminations with restrictive screen-like features, and condensation accumulations within the duct (due to non-insulated ducts traveling through cold spaces such as crawl space or attic) and incorrect pitch.

Dryers discharge moisture-laden air and lint to the outdoors, therefore dryer exhaust ducts pose little to no indoor air quality issues beyond drawing exhaust air from the surrounding environment. Restricted dryer exhaust duct systems can create fairly serious operational performance issues. In addition to accumulated lint, improperly installed dryer exhaust ducts can condense water inside the duct, and in some cases will contain accumulated liquid water as well. This condition, combined with lint, can result in cementitious masses adhering to the inside of the dryer exhaust duct system.

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