Free interactive tool
Heat Loss Calculator
Q = U·A·ΔT — watch single glazing leak and insulation pay for itself.
Watch heat leak through a wall you chose
Pick the construction, size the surface, set the temperatures; the leak in watts follows Q = U·A·ΔT.
Insulation is subtraction you can buy: the U-value is the only part of the equation the weather does not control, which is why upgrades pay every hour they exist.
- Compare single and triple glazing on the same window.
- Halve the temperature difference — what happens to the loss?
Heat escapes at a rate set by three numbers: the construction's U-value, the surface area, and the temperature difference. Only the U-value is yours to change permanently — which is the entire case for insulation.
Compare single glazing (U≈5.7) with triple (U≈0.8) on the same window and read the difference in watts and monthly kilowatt-hours.
What is a U-value?
Watts lost per square meter per degree of temperature difference — lower is better.
Where do homes lose most heat?
Typically roofs and walls by area, windows by intensity — this tool shows why windows punch above their size.