Composite Wall Heat Transfer

T1

T2

L1

L2

k1

k2

T2

T1

R1=L1/(k1A)

R2=L2/(k2A)

T

Note: In the US, insulation materials are often specified in terms of their thermal resistance in (hr ft2 °F)/Btu ----> 1 Btu=1055 J.

R-value = L/k, R-11 for wall, R-19 to R-31 for ceiling.

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