The heat transfer number “U-value” represents the heat transfer through a material as a function of the temperature gradient between the warm and the cold side. The U-value calculator can be used to measure the heat loss with one or several insulating materials. The unit of the U-value is W/m²K (watts per square meter and per Kelvin) and indicates the heat flow through an area of one square meter with a temperature difference of one Kelvin (= 1°C). The higher the U-value, the worse the insulation effect, the lower the U-value, the better the insulation effect.
The U-value calculator is for guidance. Heat transfer resistances of the air are not considered.