Underwriters Laboratories completed a 2006 fact finding study that shows a dramatic improvement in air flow
when using the new long-turn dryer venting elbow versus a typical sectioned duct elbow. One of the
findings is that it takes six long turn dryer elbows to have the equivalent affect on flowrate as a single sectioned elbow.
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.
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.
504.6.4: 35 feet less 5 feet for each typical 90 degree elbow and 1.5 feet for each 10" radius elbow.*
M1502.4: 35 feet less 5 feet for each typical 90 degree elbow and 1.5 feet for each 10" radius elbow.*
* Dryer-Ell Model LT90 Actual Length is 1.5 Feet
504.6.4: 35 feet less 2.5 feet for each typical 45 degree elbow and .75 feet for each 10" radius elbow.**
M1502.4: 35 feet less 2.5 feet for each typical 90 degree elbow and .75 feet for each 10" radius elbow.**
** Dryer-Ell Model LT45 Actual Length is .75 Feet
Current Allowable Duct Length Under Dryer Venting Code
Based on accepted ASHRAE methodology for calculating friction loss in ducts and fittings, this new elbow provides key benefits to the builder
and tradesmen by removing the reduction consequence found in most building codes. Section
M1502.6 of the 2006 International Residential Code, Section 504.6.4 of the 2009
International Mechanical Code and Section M1502.4 of the 2009 International Residential Code all permit large radius