Give water a path and it will take it

摘要

But which path? When I first was learning about hydronics, a guy I worked with, who was 15 years older than I was, told me to imagine myself as a marble moving through the pipes. He'd have me feeling the friction as I rolled along the inner surfaces of those pipes. "Here, walk down the hallway and rub your right arm against the wall," he'd say. "Feel the heat? That's friction." That sure worked for me.