U Factor

What is U Factor?

Definition of U Factor in Construction
The measurement of heat transmission through a door or window from the interior to the exterior. The lower the U value the more insulating properties in the element being measured. This is opposite the R value or rating of an assembly ,which is the insulating properties of material systems. In regard to the R value, the higher the value, the greater the insulating properties. The U factor is a measurement of an assembly and not just a material. This is why the U factor is very important when identifying the heat and cooling requirements or areas within a structure. The entire assembly is identified and tested, prior to being given a U value. Mechanical engineers and designers are commonly involved with the U value of assemblies to properly design and recommend mechanical heating and cooling systems.