Window & Glass U-Values
What is a U-Value?
A U-Value is a measurement of insulation in general the lower the value the more efficient the window as less fabric heat is lost through the glass or frame. U-values are measured in w/m2K which is the units of watts per square metre per degree Kelvin or in other words the amount of heat loss through a 1 square metre of material for every degree difference in temperature between the inside and outside. As a measurement to compare to a single 4mm pane of glass center value is 5.4w/m2K.
How are U-Values Calculated?
Q = U x A x dt
U = Q
Center Pane VS Whole Window U-Value
One of the most misunderstood concepts in double glazing is u-values and how they are measured. below shows the difference in areas that are tested.
Center Pane Whole Window
Center Pane or whole window Calculations, everything you need to know about U-Values
The center pane only takes in the center of the glass, where as a the whole window calculation takes in the glass, the spacer bar, the window outerframe and sash PVC as well as the reinforcing. The difference between a center pane and whole window can be anywhere between 0.2 and 0.4 so just make sure the when you compare value they are using the same measure.
Center Pane U-Value = 1.72 w/m2K
Whole Window U-Value = 2.0 w/m2K
The table below show the typical Centre pane u-values given by Pilkington
30th June 2011
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