Our home has a heated greenhouse attached to it. The idea is brilliant but the execution was poor. We lose a LOT of household heat through the greenhouse. We can't just let it get real cold in there because it is also our bathroom and the pipes would freeze (not to mention how uncomfortable baths and showers would be).
I imagine the people who built it thought the sunlight would warm the bathroom in winter. If it were double-paned and somewhat sealed I think it might. As it is, it just pours heat out into the great state of West Virginia. When snow falls on the greenhouse, it melts, and makes fantastic icicles.