The idea of district heating can be traced back to Roman hypocausts, some of which warmed multiple buildings. They were reintroduced into Europe during the Renaissance and slowly evolved into modern hot air, hot water, and steam heating systems. Major heating milestones are summarised, along with requirements to conserve fuel and abate smoke. Early district-heating proposals in London (1623 and 1820s), Pennsylvania (1869), Warsaw and Zurich (1872) are discussed, as are steam systems actually installed at the US Naval Academy (1853), the Philadelphia Centennial Exposition, and a hot water cogeneration system at the Banstead Downs Asylum in England (1876). Birdsill Holly - a Lockport, New York inventor - installed the first successful commercial district heating system there in 1877. by 1980, more than 50 were installed, many of which are still operating today. District cooling began shortly after that, with successful introduction of systems using brine and ammonia.

KEYWORDS: year 1995, history, district heating, district cooling