Building Code
In an effort to reduce the number of dryer fires (over 15,500 per year in the US alone) most building code has strict guidelines for properly venting a dryer. Every foot of duct run reduces airflow efficiency and small radius elbows have an even greater impact.
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State Certifications
While some municipalities are working through the process of adopting relevant code, they often accept engineering reports clarifying the improvement in airflow efficiency to allow an exception when non-specific elbow penalties are in place.
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ASHRAE Calculations
ASHRAE Fundamentals Handbook has a methodology for calculating the friction loss in ducts and fittings. Based on these formulas Dryer-Ells can be measured the same as straight pipe. This permits use of the maximum allowed run length.
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UL Fact Finding Study
Underwritings Laboratories prepared a fact find report which shows, among other findings, that Dryer-Ells are 500% more airflow efficient than sectioned, small radius elbows.
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