Boilers generate steam heat or distribute hot water for heating. Steam is a relatively old and inefficient heating technology. Today, hot-water radiators -- both in baseboards and vertical units -- are more efficient and popular. They are quiet and energy-efficient, particularly when used with separate temperature controls for different areas of the home. However, hot-water radiators slowly and unevenly distribute heat from the edges of the room. They also pose challenges for furniture placement because baseboard vents should not be blocked.