Europe's Come-to-AC Moment

In stifling apartments and sweaty row houses in England, Germany, and even Scandinavia, some Europeans are considering a very American idea: They really need an air conditioner.

One of their most accessible options, though, might feel unfamiliar to anyone accustomed to central air. Among Europe's commonly used types of air conditioning is a clunky, inefficient unit that stands a few feet high and has a wide exhaust tube meant to go out a window. Such units are typically "a panic-buy on a hot weekend," Brian Motherway, the head of energy efficiency at the International Energy Agency, told me. People grab the first machine they see and end up living with it for a decade, he said...