Quantify heating/cooling savings from upgrading glazing using U-values, HDD/CDD, HVAC performance, and energy prices. Designed for fast feasibility checks and client-ready outputs.
Inputs
Preset scenarioCustom
Window area & climate
Total window area300 ft²
Use the total glazed area you plan to upgrade (not wall area).
Area unit
Switching units preserves the physical area.
Heating Degree Days (HDD)4,500
Annual HDD (base ~18°C / 65°F). If unknown, use the presets.
Cooling Degree Days (CDD)1,100
Annual CDD for conductive cooling impacts (solar gains not included).
Window U-values
Current window U-value1.30 W/m²·K
Upgraded window U-value0.80 W/m²·K
HVAC & energy prices
Heating system
Heating performanceCOP 3.0
For heat pumps use seasonal COP (2.0–3.5 typical). For gas use AFUE as a fraction (0.85–0.97).
Electricity price$0.15/kWh
Gas price$1.50/therm
Project economics
Incremental installed cost$6,000
Enter the extra cost of the upgrade (e.g., triple vs double), not the full window replacement price.
Energy escalation / year2.5%
Used for NPV/cashflow only.
Analysis horizon20 years
Discount rate5.0%
This tool models conductive heating/cooling impacts using U-values and degree days. Solar gains (SHGC), shading, and air leakage can dominate in some climates.