Although not specifically intended as heat emitters, the copper tubing connecting the components of many hydronic systems certainly does release heat to its surroundings, compromising the system's ability to deliver heat precisely where and when it's needed.
Although not specifically intended as heat emitters, the copper tubing connecting the components of many hydronic systems certainly does release heat to its surroundings. Sometimes designers disregard this heat output, assuming it's trivial relative to the heat released by the real heat emitters. Some might point out that if the tubing travels through heated space, the heat released is not really "lost" heat, it's heat delivered to the space by the tubing rather than the intended heat emitter. That may be true at times, but it still compromises an important and fundamental benefit of hydronic heat--the ability to deliver heat precisely when and where it's needed.