How to use the window heat loss calculator
Estimate heat lost through a window and the energy lost in a day. Enter window u-value, window area, indoor-outdoor temperature difference in the fields above; the heat loss, energy lost per day are computed instantly and plotted on the chart so you can see how the answer changes.
Common searches this calculator answers include “window heat loss”, “cold window draught energy”, “window U value heat”, “calculate window heat loss”, “find heat loss”.
Formula
Variables
- U — Window U-value (W/(m²·K))
- A — Window area (m²)
- dT — Indoor-outdoor temperature difference (K)
Worked example
With window u-value = 2.8 W/(m²·K), window area = 3 m², indoor-outdoor temperature difference = 20 K, the calculator gives heat loss ≈ 168 W; energy lost per day ≈ 4.032 kWh.
Frequently asked questions
What is the window heat loss calculator used for?
Estimate heat lost through a window and the energy lost in a day. It helps with questions such as “window heat loss”, “cold window draught energy”, “window U value heat”.
What is the formula for the window heat loss calculation?
Heat loss (W) = U × A × dT. Energy lost per day (kWh) = [Heat loss] × 24 / 1000. Here U is window u-value (W/(m²·K)), A is window area (m²), dT is indoor-outdoor temperature difference (K).
What inputs do I need for the window heat loss calculator?
You need window u-value in W/(m²·K), window area in m², indoor-outdoor temperature difference in K. Each field is pre-filled with a typical example so you can see how the result responds as you edit the numbers.
How do I use the window heat loss calculator?
Type values into the input fields. Results and the chart update instantly. Use Reset to restore the example values, Copy results to paste them elsewhere, or Share to copy a link that preserves your inputs.
Is the window heat loss result exact?
Calculations use standard formulas and double-precision arithmetic, then display about seven significant figures. Real-world measurements carry uncertainty, so treat results as estimates unless your inputs are exact.