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Measure and calculate window sizes
In Climate Zone 6, insulation (low U-factor) is most important for windows.
Climate Zone
6
Electricity
$0.18/kWh
Labor Costs
100% avg
Calculate window sizes from opening measurements or vice versa
Vermont is in Climate Zone 6 - Cold (heavy heating, light cooling). Homes here typically have higher heating demands than cooling.
Window sizing involves two key measurements:
The rough opening is the framed hole in your wall. The window unit is smaller—typically 1/2 to 1 inch narrower and shorter than the opening. This gap is needed for shimming, leveling, and foam insulation.
For replacement (insert) windows, measure inside the existing frame at top, middle, and bottom for width; at left, center, and right for height. Use the smallest measurements and check that the frame is in good condition.
Nominal size is a standard designation, not the exact measurement. A 3040 window (30×40) isn't exactly 30 inches wide—it's designed to fit a rough opening of about 30.5×40.5 inches. Always check actual unit dimensions.
Yes, but it requires removing framing and may need a structural header if you're widening significantly. Making it smaller is easier—just add framing lumber. Either change affects the wall and needs proper support.