How efficient is thermal break window?
The good news is that there's actually a more or less objective way to compare them these days. To ensure that homeowners could compare manufacturers and products equally, an industry-wide standard for rating and labeling windows was established in 1992. The National Fenestration Rating Council (NFRC) label shows you the thermal insulating performance based on U-factors. That rating assures that the entire window unit has been tested, not just the glass or other components -- important since they work together as a system.
Here's some representative numbers for you to compare... and remember, lower is better...
Glazing [value in aluminum] (value in wood or vinyl)
Regular Single Pane [1.30] ( 0.94)
Regular Double Pane [0.81] (0.51)
Double Pane with typical Low-E Glass [0.70] (0.42)
Double Pane with Low-E & Argon Blend [0.64] (0.37)
Regular Triple Pane [0.72] (0.43)