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Free double glazing savings calculator. Estimate annual HVAC dollar savings when replacing older windows with double- or triple-glazed low-U assemblies, using your total heating and cooling spend, an approximate share due to windows, and before and after U-values. Explore more in our energy and sustainability calculator category.
Last updated: April 18, 2026
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Rule-of-thumb often falls in roughly 15–35% for older homes; use an audit if you have one.
Single-pane clear often near ~1.0+.
Good double low-E often roughly 0.25–0.40.
Modeled HVAC savings
$374
≈ 15.6% of total annual HVAC cost
Attributed to windows (before)
$528
Window loss reduction
70.9%
Model limits
Delta U
Strong savings
Moving from high-U single glazing to modern insulated units increases modeled fractional improvement.
Scale
Annual $ up
The same percentage improvement applies to more dollars when baseline HVAC cost is larger.
Input
Window %
Replace the default window-loss percentage with your model or auditor recommendation.
U_new
Typical 0.2–0.3
Enter the assembly U-factor from the manufacturer label for triple units.
Note
U-value only
Tighter installs reduce infiltration; combine with a weatherization calculator for stack effects.
ROI
Project cost
Divide installed window cost by annual savings for simple payback using our insulation payback tool pattern.
Default scenario: modeled annual savings about $374 (15.6% of total HVAC).
The calculator multiplies annual heating and cooling cost by your chosen percentage attributed to window heat loss and gain. It then applies the conductive improvement factor (U_old minus U_new) divided by U_old to that window-related cost. This assumes the share and U-values are consistent with your climate and home; it does not replace hourly simulation.
Window cost ≈ HVAC × (window % ÷ 100)Savings ≈ Window cost × (U_old − U_new) ÷ U_oldUse labeled U-factors for the exact products you are pricing.
Share it with homeowners comparing window upgrades
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