Dryer-Ell Performance Advantage
UL found that you would have to use six Dryer-Ell LT90s to affect airflow rate as much as one sectioned elbow. Its long radius and smooth interior reduce friction loss and improve duct performance.
Sectioned Dryer Elbow Duct-length Equivalency
Further, the study found the actual affect of sectioned dryer elbows is equivalent to 15 feet of straight pipe.
Dryer Vent Duct Run Impact - Current Code
Length of run Penalties under Current Dryer Venting Code
Most code, today, still reflects only a five foot reduction in length-of-run for every ninety degree turn in the duct. This seeming disparity, however, is somewhat offset by the very short overall run length allowed (most dryer OEMs allow longer). There are proposals before the ICC to bring both variables closer together. For now, there is a 5 foot reduction for every typical elbow from an overall 35 feet in allowable length.
35 feet less 5' for each typical 90 degree elbow and 1.5' for each 10" radius elbow.*
25 feet less 5' for each typical 90 degree elbow and 1.5' for each 10" radius elbow.*
35 feet less 2.5' for each typical 45 degree elbow and .75' for each 10" radius elbow.**
25 feet less 2.5' for each typical 90 degree elbow and .75' for each 10" radius elbow.**
Current Allowable Duct Length Under Dryer Venting Code
Section M1502.6 of the 2006 International Residential Code, Section 504.6.4 of the 2009 International Mechanical Code, Section M1502.4 of the 2009 International Residential Code, Section 504.6.4 of the 2012 International Mechanical Code and Section M1502.4 of the 2012 International Residential Code all permit large radius elbows.
Click HERE for Calculations and Engineering Reports.
The reduction in friction loss provides important benefits for venting in residential construction.