certificate for low-e? ways of testing? ways of knowing?

i hace low-e glass (6+6/ 10 low-e/ 6) installed in house in south of Spain. this summer, the low-e glass heated up noticably more then similar panes of glass, on same orientation and exposure of less performing stratification (6+6+6).
is this acceptable?
can i be sure about the quality installed?
any suggestiones?
geert-hugo