A greenhouse can be added to your house as a passive solar heater. During the coldest days of the winter, a greenhouse will stay 15 to 25 degrees warmer than the outside at night. On a clear cold day it will heat up to 80 degrees if it’s 30 outside. During the spring and fall, a greenhouse makes a very pleasant sitting room. During the summer, the roof vents should be opened and the roof covered with deciduous vines or bamboo screen to make a nice well-ventilated, shady area.