Since your grandparents plan to stay at the cabin often and they like it warm, you decide that you need to be able to achieve 23 C in the winter. Assuming a minimum heat output of 2 people, 2 lamps, a TV, a computer and a refrigerator, you've figured out that a reasonable estimate for total internal gain rate is 600 W. You calculate that the whole building heat transfer coefficient for the existing cabin is 400 W/K. How much will it cost annually to heat the renovated cabin with the gas stove, assuming the stove is 78% efficient, gas costs $2.00/therm, and the whole building heat transfer coefficient of 200 W/K? (1 therm = 105,480 kJ). Assume that the Annual Heating Degree Days for the correct tbp is 5290 HDD (C-day). Don't forget the efficiency of the stove, and check your units carefully - it will help avoid mistakes! Also think carefully about the concept and equation for efficiency before just plugging in numbers - should the energy you pay for be more or less than what goes into heating the house? What makes sense