While studying for his Ph.D. in electrical engineering at Columbia University six or seven years ago, Marshall Cox regulated his room’s temperature in winter the way most New Yorkers with steam radiators do. He opened a window.

But then his twin brother, Jeremy, moved to New York to dance in “Come Fly Away” on Broadway. His brother complained “incessantly,” Mr. Cox said, that “it was boiling, or freezing, many times both over the course of a night.” It drove Marshall Cox to invent the Cozy, a radiator cover that can contain the warmth in an overheated room and shift it to an underheated room. The Cozy, which Mr. Cox has described as a “glorified oven mitt” and which is being sold on a limited basis, went on to win a $220,000 M.I.T. Clean Energy Prize in 2012.

The Cozy’s victory is understandable. It addresses a problem that has afflicted New Yorkers since the early 1900s, when oversize radiators were necessitated by a Board of Health directive requiring open windows on even the iciest winter days. This was back when “fresh air” was considered the universal cure-all.

Today’s apartment and condominium dwellers needn’t suffer, though. Thanks to modern technology, energy-saving programs, and a handful of tradesmen versed in century-old plumbing techniques, there are a variety of fixes to tame runaway radiators.