Heat conduction calculator
Steady conduction is proportional to area and temperature difference and inversely proportional to thickness.
W/(m K)
Mineral wool 0.04; brick 0.7; concrete 1.7; glass 1.0; steel 50; copper 400.
m2
K
Heat flow
160W
- U-value
- 0.400 00 W/(m2 K)
- R-value (SI)
- 2.500 00 m2 K/W
- R-value (imperial)
- 14.196 ft2 F h/Btu
- Heat flux
- 8.0000 W/m2
- Energy lost per day
- 3.840 kWh
Show the working
- Thermal conductivity = 0.04
- Area = 20
- Thickness = 0.1
- Temperature difference = 20
- U-value = 0.04 / 0.1 = 0.4
- Heat flow = 0.4 * 20 * 20 = 160
- R-value (SI) = 0.1 / 0.04 = 2.5
- Heat flux = 0.4 * 20 = 8
- Energy lost per day = 160 * 24 / 1000 = 3.84
- R-value (imperial) = 2.5 * 5.678263398 = 14.1957
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- Q = k A dT / L
- U = k / L, R = L / k
- Imperial R = SI R x 5.678263398
This is conduction through the material alone. A real wall also has surface resistances on each face, which a full U-value calculation adds.
The imperial R-value is a different unit, not a different number — R-13 imperial is R-2.3 in SI.