In the staff report SDStaff McCaff and SDStaff Manhattan replied to inquiry of steam from manhole covers in U.S.:
"Yup, here in the U.S. we’ve got the Straight Dope, steam rising from the streets, and Starsky and Hutch. All that a truly progressive civilization requires.
As for what people put down there that causes steam to rise … why, they put steam, of course. Large steam plants tended to be more efficient than small ones, and some industries have waste heat, so, where the density is high enough to support it, you may find centralized steam plants selling heating steam to their neighbors, distributing it in underground insulated pipes."
We have distribution of heat and even cold throught Helsinki here in Finland but we don’t have steam rising from manhole covers not even during the coldest months. The reason is that those pipes are so well insulated that the heat stays inside the pipes and is not wasted during the flow.
So I have a question: Why does steam rise from manhole covers in U.S.?