U-value (Thermal Transmittance)
The U-value is the rate of heat transfer through a structure per unit area and temperature difference, in W/m²·K. A lower U-value means less heat loss. It combines the insulating effect of all layers and surface coefficients into one figure.
U-value is the inverse of total thermal resistance and lets you compare assemblies on a like-for-like basis. For insulated industrial equipment it captures the combined effect of the insulation λ, thickness and surface conditions, and is used to estimate heat loss and the temperature drop a given insulation achieves.
Related terms
Thermal Conductivity (λ) · Emissivity (ε) · Waste Heat Recovery
Related guides
Industrial heat loss and insulation
Why bare hot surfaces are a bigger loss than most plants realise, how to estimate it, and why valves and flanges are the usual culprits.
How to improve boiler efficiency
The practical levers that move boiler efficiency — combustion, blowdown, feedwater, flue-gas heat and standing losses — and how to find them.