Window replacement energy savings calculator

Estimate annual heating energy saved by replacing windows with a lower whole-window U-value. U-value measures how easily heat passes through a window, including its frame. Lower values mean less heat passes through under the same conditions. Use comparable ratings for the existing and proposed windows.

Enter the total area being replaced in square metres. Use heating degree days in Celsius-days from a local weather record or assessment. Degree days combine how cold it was and for how long, compared with a chosen base temperature. Keep that base consistent with the heat assessment.

Enter the heating system's efficiency fraction or heat pump COP, the price per kWh of purchased heating energy and the installed window quote. The result shows useful heat saved, purchased energy avoided, yearly cost saving and simple payback. It covers heat passing through the windows, rather than every possible effect of replacement.

Annual transmission heat saved = window area × (old U-value − new U-value) × heating degree days × 24 ÷ 1000. Purchased energy saved = useful heat saved ÷ heating efficiency fraction or COP. Price only the avoided purchased energy.

Use 0.90 for a heater with 90% efficiency. This field is already a fraction, so do not enter 90 or divide 0.90 by 100 again. For a heat pump, enter its assessed COP directly. COP is heat delivered divided by electricity used; a ratio of 3 means 3 kWh of heat per 1 kWh of electricity.

The factor 24 converts degree days to degree hours, and dividing by 1000 converts watts to kilowatts. Price the purchased energy in cents per kWh, then divide by 100 for Canadian dollars. A replacement with a higher U-value produces a negative heat and cost saving; the calculator does not turn that into a positive result.

These illustrative inputs are separate from your saved answers. Prices, use and performance are held constant for this worked scenario; they are not personal defaults.

Use whole-window values measured on a comparable basis. Glass-only values leave out the frame and cannot stand in for a whole-window rating. Match the area measurement to the products being compared so the same window is not counted twice.

The estimate excludes changes in air leakage, solar heat gains, cooling, shading and installation effects. It does not assess draughts, moisture, noise or comfort. Heating degree days describe the chosen weather period; they do not predict every future year.

Simple payback divides the entered installed price by positive annual energy savings. Zero or negative savings have no finite payback. It holds prices and performance constant and excludes finance, replacement and future changes. Existing fixed heating charges are not savings from lower consumption. Money is rounded only for display. Incomplete edits retain the last valid estimate with a warning.

Canadian prices vary by province, utility and plan. Enter the heating energy price in cents per kWh, including applicable usage charges and tax. Convert a gas price per cubic metre using the matching bill energy content before entry.

Dividing a complete bill by consumption can include fixed fees that will not change after window replacement. Use the price for energy actually avoided. Source dates describe the recorded method or data; they do not verify your personal quote or window ratings.

Ask a qualified energy adviser or window installer to check the window area, whole-window ratings and local heating degree days. Ask which savings the quote attributes to heat transmission and which depend on air sealing or other work.

Confirm installation details, moisture control and any building requirements before proceeding. The calculator cannot inspect the opening, approve a product or confirm safe installation. Consider the complete project scope alongside the energy estimate when comparing quotes.