U-Values - European versus Australian

U-value calculations are not the same the world over. Australia has decided to follow the American NFRC (National Fenestration Rating Council) system when making calculations for the Window Energy Rating System - WERS.

U-value measures how well a product allows heat to pass through. It is a measure of the rate of non-solar heat loss or gain through a material or assembly. The lower the U-value, the greater a window's resistance to heat flow and the better its insulating value. The whole window assembly is tested which includes the effect of the frame, glass, seals and any spacers.

What does it mean that U-values differ from continent to continent? If you import windows and doors from Europe they will have a very low U-value number, lower than any U-value for windows made here in Australia. Do you get a better product? No, not necessarily. You might get the exact same product, with the U-values just calculated differently. Or you may get a better product in Australia, just with a higher number.

The AWA Australian Windows Association writes; "Performance calculations utilise different protocols to create their window performance data. In Europe windows are calculated to CEN protocols which utilise different temperature conditions to find the performance data of their windows. The windows will have different results to the performance data conducted in Australia."

In Australia window sizes for U-value testing are 600mm wide x 1500mm high = 0.9m², in Europe the size tested is up to 2.3m² (1.23x1.48m). This means that in Europe the frame itself is a much smaller percentage in comparison to the glass than in Australia, hence another reason why U-values vary.