Chapter 1, Problem 57EP

The north wall of an electrically heated home is 20ft long, 10ft high, and 1ft thick and is made of brick whose thermal conductivity is $k=0.42{\text{ Btu/h}}^{\text{.}}\text{ft}{\text{.}}^{\circ }\text{F}\text{.}$

On a certain winter night, the temperatures of the inner and the outer surfaces of the wall are measured to be at about ${62}^{\circ }\text{F}$ and ${25}^{\circ }\text{F,}$ respectively, for a period of 8 h. Determine (a) the rate of heat loss through the wall that night and (b) the cost of that heat loss to the homeowner if cost of electricity is $0.07/kWh.