Doubling insulation thickness L affects conduction through a wall; what happens to heat transfer?

Doubling insulation thickness L affects conduction through a wall; what happens to heat transfer?

• A. Doubles Q
• B. Quadruples Q
• C. Halves Q
• D. Stays the same

Answer: (C)

Heat transfer by conduction through a flat wall is inversely related to the thickness of the insulating layer. The rate of heat flow is given by Q = (k A ΔT) / L, where k is the material’s thermal conductivity, A is the area, ΔT is the temperature difference, and L is the thickness. If you double the insulation thickness, L becomes 2L, so Q becomes (k A ΔT) / (2L) = (1/2) Q. In other words, heat transfer is halved. The thicker the insulation, the greater the thermal resistance, which slows down heat flow.

Heat transfer by conduction through a flat wall is inversely related to the thickness of the insulating layer. The rate of heat flow is given by Q = (k A ΔT) / L, where k is the material’s thermal conductivity, A is the area, ΔT is the temperature difference, and L is the thickness. If you double the insulation thickness, L becomes 2L, so Q becomes (k A ΔT) / (2L) = (1/2) Q. In other words, heat transfer is halved. The thicker the insulation, the greater the thermal resistance, which slows down heat flow.