Compare window heat loss, cooling demand, payback, and emissions. Enter project data. See annual savings and long term upgrade value.
| Project Type | Area ft² | Old U | New U | HDD | CDD | Installed Cost |
|---|---|---|---|---|---|---|
| Small Home Upgrade | 180 | 1.10 | 0.32 | 3800 | 950 | $4,800 |
| Cold Climate Home | 320 | 1.25 | 0.28 | 6200 | 500 | $8,900 |
| Mixed Climate Office | 760 | 1.05 | 0.35 | 3100 | 1800 | $18,500 |
Heat transfer reduction:
ΔU = Old U-Factor − New U-Factor
Annual heating energy saved:
Heating Saved = ΔU × Window Area × HDD × 24 ÷ 3412 ÷ Heating Efficiency
Annual cooling energy saved:
Cooling Saved = ΔU × Window Area × CDD × 24 ÷ 3412 ÷ COP
Annual money saved:
Annual Savings = Heating Saved × Heating Cost + Cooling Saved × Electricity Cost − Maintenance Change
Simple payback:
Payback = Net Project Cost ÷ Net Annual Savings
Net present value:
NPV = −Net Cost + Σ Annual Savings ÷ (1 + Discount Rate)year
Enter the total window area being replaced. Use square feet for the area.
Add the old window U-factor. Then enter the new window U-factor.
Use local heating degree days and cooling degree days. These values describe climate demand.
Enter heating system efficiency. Use COP for cooling equipment performance.
Add energy prices, installed cost, rebates, and any yearly maintenance change.
Press the calculate button. Results appear above the form.
Use the chart to compare yearly savings against project cost.
Download the CSV or PDF report for record keeping.
Windows affect heat movement through a building envelope. Old glass, weak frames, and air leaks can raise heating and cooling demand. A better window reduces this transfer. The U-factor is the main physics value here. A lower U-factor means less heat passes through each square foot. This calculator compares the old and new values. It then connects that change to local climate data.
Heating degree days estimate how much heating is needed through the year. Cooling degree days estimate cooling demand. More degree days usually mean greater savings from efficient windows. The calculator multiplies the U-factor difference by window area and degree days. It also converts British thermal units into kilowatt-hours. This gives a practical annual energy estimate.
Energy savings alone do not show the whole project value. Installation cost, rebates, energy prices, and system performance matter. Simple payback tells how many years are needed to recover net project cost. Net present value adds a discount rate. This helps compare future savings with money spent today.
Efficient windows may also lower carbon emissions. The calculator multiplies saved energy by an emissions factor. You can adjust this factor for your local power or fuel mix. This result is useful for sustainability reports. It also helps compare window upgrades with insulation, HVAC, or sealing projects.
Treat the output as a planning estimate. Actual savings can vary. Air leakage, shading, solar gain, occupant behavior, and thermostat settings may change results. For stronger accuracy, use measured utility bills and local climate data. Still, this tool gives a clear first estimate. It helps decide whether replacement windows are financially and physically sensible.
U-factor measures heat transfer through a window. A lower number means better insulation and less heat loss or heat gain.
Larger window area allows more heat movement. Replacing more glass usually creates larger potential energy savings.
Heating degree days estimate yearly heating demand. Higher values mean colder climates and greater heating savings potential.
Cooling degree days estimate yearly cooling demand. Higher values mean warmer climates and greater cooling savings potential.
Simple payback is useful, but limited. Net present value gives a better long-term financial view.
Heating equipment converts purchased energy into useful heat. Lower efficiency means more purchased energy is needed.
COP means coefficient of performance. It shows cooling equipment efficiency. Higher COP means less electricity for cooling.
No. Results are estimates. Weather, air leakage, solar gain, shading, and user behavior can change actual savings.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.