The main difference between a three season sunroom and year-round sunroom is the number of months you can comfortably use the space each year.  A Three Season sunroom can be used 10 to 11 months out of the year. While a year-round sunroom, including heating and air conditioning, can be used all year long. The main differences between the two sunrooms is that a year-round sunroom has elements that allow you to better manage extreme heat and cold temperatures. A year-round sunroom includes: insulated glass, insulation in the roof and the foundation, and a heating and cooling system.