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Compare window energy efficiency ratings
In Climate Zone 5, insulation (low U-factor) is most important for windows.
Climate Zone
5
Electricity
$0.24/kWh
Labor Costs
125% avg
Compare energy efficiency between window types
Massachusetts is in Climate Zone 5 - Cool-Humid/Cold (significant heating, moderate cooling). Homes here typically have higher heating demands than cooling.
U-value measures heat transfer through the complete window assembly:
In cold climates (heating dominated), aim for 0.25 or lower. In moderate climates, 0.30-0.35 is usually sufficient. In hot climates, U-value matters less than SHGC, but 0.40 or better is typical for Energy Star.
They measure the same thing inversely. R-value measures resistance to heat flow (higher is better); U-value measures heat flow rate (lower is better). R = 1/U. A U-value of 0.25 equals R-4.
Yes, significantly. Low-E coatings reflect radiant heat back, reducing heat transfer. A double-pane clear glass window might be U-0.50; adding Low-E drops it to U-0.30. Adding argon gas improves it further to about U-0.27.
In very cold climates (Zone 6-7) with high heating costs, often yes. In moderate climates, the 15-25% price premium rarely pays back through energy savings. The extra cost might be better spent on air sealing or insulation.