Model LT90 delivers improved airflow efficiency for ninety degree turns. It is a straight pipe equivalent for most building code including 2009 and 2012 IMC and IRC.
LT90 Technical Specifications
LT90 Installation Instruction
The Dryer-Ell has a four-inch diameter (the standard for dryer duct pipe) and an eighteen-inch overall length. Because it is code approved to eliminate run-length penalties, the LT90 is very useful for taking advantage of the maximum allowable exhaust duct length. Its longer radius and smooth interior improve dryer performance and are 500% more airflow efficient than sectioned elbows.
Based on the fundamentals handbook methodology for calculating friction loss, the LT90 has an equivalent length of 1.5 feet (or its actual length). You may find full formula details and independent engineering confirmation in the White Papers / ASHRAE Calculations sections. These calculations are recognized in 2006 IRC under section M1502.6 (2009 and 2012 IRC and IMC list the actual length as discussed below).
International Code Council Adoption
2009 International Mechanical Code and International Residential Code now include tables eliminating the run length reduction required for standard elbows when using a Dryer-Ell alternative. Now, instead of having to show the full ASHRAE based airflow effect, the tables clearly show that a ten inch radius smooth 45 degree elbow has an equivalent length of 3/4 feet (LT45's actual length).
|Dryer Exhaust Duct Fitting Type||Equivalent Length (feet)|
|4” radius mitered 45 degree elbow||2-1/2|
|4” radius mitered 90 degree elbow||5|
|6” radius smooth 45 degree elbow||1|
|6” radius smooth 90 degree elbow||1-3/4|
|8” radius smooth 45 degree elbow||1|
|8” radius smooth 90 degree elbow||1-7/12|
|10” radius smooth 45 degree elbow||3/4|
|10” radius smooth 90 degree elbow||1-1/2|