Condensation risk calculator
Steady one-dimensional surface estimate only. It excludes ice/frost, thermal bridges, interstitial moisture, changing conditions over time, air leakage, and standards or code compliance. A result is not a building assessment.
A QUICK WALKTHROUGH
How to use this tool
- Indoor air temperature (°C)
- Indoor relative humidity (%)
- Outdoor air temperature (°C)
- Assembly U-value (W/m²·K)
- Interior surface resistance Rsi (m²·K/W)
- Your minimum temperature margin above dew point (°C)
Calculation
Water dew point uses the Magnus equation: γ = ln(RH/100) + 17.625T/(243.04+T), Td = 243.04γ/(17.625−γ). Estimated surface temperature is Ti − U·Rsi·(Ti−To). The comparison uses only the threshold you enter.
Scope and assumptions
Steady one-dimensional surface estimate only. It excludes ice/frost, thermal bridges, interstitial moisture, changing conditions over time, air leakage, and standards or code compliance. A result is not a building assessment. Inputs stay in this browser and are not uploaded or stored. Water Magnus coefficients 17.625 and 243.04 are reported for -40 to 50 °C: https://rmets.onlinelibrary.wiley.com/doi/10.1002/qj.4609.
GOOD TO KNOW
Common questions
Does this certify that a wall is safe from condensation?
Steady one-dimensional surface estimate only. It excludes ice/frost, thermal bridges, interstitial moisture, changing conditions over time, air leakage, and standards or code compliance. A result is not a building assessment.