Heat conduction through a plane wall
Fourier’s law for a plane wall under steady one-dimensional conditions is Q = kA(T₁ − T₂)/L.
Here k is thermal conductivity, A is area, and L is thickness. Doubling wall thickness halves heat flow when the other variables are constant.
Practice: for k = 2 W/(m K), A = 1 m², ΔT = 20 K and L = 0.1 m, Q = 400 W.