Holly District Heating System

site of the first US district heating steam-heating system

As a means of avoiding the basic inefficiency of heating buildings with individual small boilers, Birdsill Holly invented the "district" steam-heating system. Its basis was a large central boiler plant that furnished steam under moderate pressure to a group of buildings in a surrounding district through a loop of supply and return mains, heavily insulated to reduce heat loss. Each customer was charged for the amount of steam consumed, determined by metering the water of condensation. The concept was highly successful. Before the end of the century a number of district heating companies had been formed, principally in large cities.