Dryer-Ell Model LT90

Model LT90 delivers improved airflow efficiency for ninety degree turns. It is a straight pipe equivalent for most building code including 2009 IMC and IRC.

LT90 Technical Specifications
LT90 Installation Instruction

This 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 aiflow efficient than sectioned elbows.

ASHRAE Calculations

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 section. These calculations are recognized in 2006 IRC under section M1502.6 (2009 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 1-1/2 feet (LT90's actual length).

Dryer Exhaust Fitting Equivalent Length
(IMC 504.6.4.1 / IRC M1502.4.4.1)
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