1. The problem statement, all variables and given/known data We are heating up the cabin log with a furnace that has strength of 4 kW. The surface of the walls of the log cabin is 35 m². What is the temperature in the log cabin, if the outside temperature is -20 °C? The thermal conductivity of wood is 0.4 W/mK; the average wall thickness is 15 cm. How many degrees will be the temperature reduced in the log cabin, if we install windows into walls, through which escapes heat flow of 1800 W, and the surface area of the windows is 10 m²? 2. Relevant equations ΔQ/Δt= K [AΔT/d] 3. The attempt at a solution First part: What is the temperature in the log cabin, if the outside temperature is -20 °C? ΔQ/Δt= K [A(T(hot)-T(cold))/d] 4000 W= 0.4 W/mK [T(hot)-253 K)/ 0.15 m T(hot)= 295.86 K= 22.7 C Are my calculations correct? Now, for the second part, I really don’t know how to approach it. I tried several times but my results didn’t make any sense (either too high or too low temperature). Can someone please help me? Thank you!