  The heat equation is considered in the complex system consisting of many
small bodies (particles) embedded in a given material. On the surfaces of the
small bodies a Newton-type boundary condition is imposed. An equation for the
limiting field is derived when the characteristic size $a$ of the small bodies
tends to zero, their total number $\mathcal{N}(a)$ tends to infinity at a
suitable rate, and the distance $d = d(a)$ between neighboring small bodies
tends to zero $a << d$. No periodicity is assumed about the distribution of the
small bodies.
