Frequently asked questions
Answers about thermal units, calculation assumptions, saved results and choosing the right tool. Check the formula and limits on each calculator page before using its result for a project.
Reviewed:
What is the difference between lambda, R and U?
Lambda is a material's conductivity in W/(m·K). RSI is thermal resistance in m²·K/W; a homogeneous layer has RSI = d/λ. U is transmittance in W/(m²·K) and uses the complete assembly resistance, including appropriate surfaces and any required corrections. US R uses different units: US R = 5.678263 × RSI. Never substitute a US R number directly for SI resistance.
Does a calculator result prove compliance?
No. These tools use their stated inputs and simplified methods. They cannot automatically verify every thermal bridge, moisture condition, structural load, cable protection or hydraulic loss. A plausible result still needs the relevant product data and project checks. Numerical precision does not imply that uncertain inputs are accurate.
Where are saved calculations stored?
When you choose to save a supported calculation, it stays in local storage in this browser. Another device or browser does not automatically receive it. Use the available backup/export workflow for records you need to keep. Clearing site data or using temporary browsing can remove the saved records. The new quick estimators show a result but do not automatically add it to saved calculations.
How can I check an unexpected result?
Record the page, input values, units and result. Reproduce the worked example first, then compare your product data and rounding with the formula. The help page provides checks you can perform yourself. There is currently no public support mailbox or report submission form.
Calculation formulas
RSI = d / λ; U = 1 / (Rsi + ΣR + Rse); RUS = 5.678263 × RSI; ΔV = I × Rloop; Qheat = A × q / 1000; Qflow = v × πD² / 4; Vconcrete = L × W × d
Use SI dimensions in these equations: thickness and diameter in metres, volume in m³, flow in m³/s and current in amperes. Heat-load area is in m² and its specific input in W/m²; the result is kW. Each linked guide gives its inputs, examples and limits. A homogeneous U-value formula does not account for framed paths or ground heat flow.