New as of August 2009, model LT45 delivers improved airflow efficiency for forty five degree turns. It is a straight pipe equivalent for most building code including 2009 and 2012 IMC and IRC.
LT45 Technical Specifications
LT45 Installation Instruction
Model LT45 has a four-inch diameter (the standard for dryer duct pipe) and a nine-inch overall length. It is particularly useful for installations where run length can be shortened by traversing the space diagonally (i.e.: attic or basement). Like the LT90, its smooth interior and ten inch radius affect flow rate to the same degree as straight pipe.
Based on the fundamentals handbook methodology for calculating friction loss, the LT45 has an equivalent length of .71 feet (or its actual length). You may find full formula details and independent engineering confirmation in the White Papers / ASHRAE Calculations section. These calculations are recognized in 2006 IRC under section M1502.6 (2009 / 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|