How do you analyze heat transfer through a composite wall using thermal resistance networks?

For a composite wall, thermal resistances are combined like electrical circuits. Series layers (convection + conduction + convection): R_total = 1/(h₁A) + Σ(L_i/k_iA) + 1/(h₂A). For parallel paths (like studs in insulation), calculate equivalent resistance using 1/R_eq = 1/R₁ + 1/R₂. Heat transfer rate: Q = ΔT_overall/R_total. Interface temperatures are found using Q×R to that point. This approach simplifies complex geometries, accounts for contact resistances at interfaces (typically 0.5-5×10⁻⁴ m²-K/W), and enables quick parametric studies for insulation optimization in building walls, industrial furnaces, and electronic enclosures.