Thermal conduction calculator
Heat flow, thermal resistance and U-value of a single layer.
Fill in the fields and the result will appear here automatically.
Calculate steady heat flow through one flat uniform layer. Enter the temperature difference between its faces; conductivity is constant. The shown coefficient k/d belongs to this layer, not a complete wall or window with surface heat transfer. Daily energy assumes the same conditions for all 24 hours.
How it works
Formula and logic
Flow = conductivity × area × temperature difference ÷ thickness. Thermal resistance = thickness ÷ conductivity, and the U-value is its reciprocal.
Example
A 10 m² wall with 200 mm of mineral wool at a 25 K difference passes 50 W.
Fields and units
- Area — m²
- Layer thickness — m
- Thermal conductivity λ — W/(m·K)
- Temperature difference — K
How to use
- — Enter the area of the construction.
- — Set the layer thickness in metres: 200 mm is 0.2.
- — Give the conductivity: mineral wool 0.04, brick 0.7, glass 1.0, timber 0.15 W/(m·K).
- — Set the temperature difference across the layer.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- OpenStax: steady conduction through a layer
- Limitation
- One-dimensional steady conduction through one layer with constant k. Surface films, radiation, thermal bridges, contact resistances and heat storage are excluded. Negative ΔT reverses flow; zero ΔT gives zero flow.
FAQ
Why does glass give such an enormous flow?
Because only the conduction of the glass itself is counted, and its resistance is negligible. A real window holds heat through the air films at its surfaces and the cavity between panes.
How do I combine several layers?
For plane layers in series with equal area, Rlayers=Σdᵢ/kᵢ. A complete assembly coefficient also needs the relevant surface and contact resistances. They depend on conditions and are not automatically inserted here.
How is this different from a heating power calculator?
That works out how much heat a room needs from its volume. This works out how much escapes through one specific construction from its conductivity.
Why can the difference be negative?
Because the flow can run inward: in summer the outside is warmer than the room. The sign shows direction; the magnitude is unchanged.