In the United States, steam district heating has been used extensively in universities, military installations, hospital complexes, and cities. However, many of the city systems have been abandoned because of competition from relatively cheap oil and natural gas. Most of the steam systems were inefficient and could not use natural gas and oil and economically serve their customers. The history of district heating in Europe is drastically different from that in the United States. The development of district heating in northern and eastern Europe started in the early 1950s. Hot water, rather than steam, was used as the transport medium and the systems have proved to be more economical.

Recently, the northern European concept has been introduced into two U.S. cities—St. Paul and Willmar, Minnesota. The hot water project in St. Paul started construction and operation in the summer and fall of 1983, respectively. The entire first phase of the St. Paul project will take two summers to construct and will connect approximately 80 buildings for a total of 150 MW(t). The system spans the entire St. Paul business district and includes privately owned offices and retail buildings, city and county government buildings, hospitals, the state capitol complex, and several industrial customers. The City of Willmar, Minnesota, replaced an old steam system with a modern hot water system in the summer of 1982. The first phase of the hot water system was constructed in the central business district. The system serves a peak thermal load of about 10 MW(t) and includes about 12,000 ft (3600 m) of network. The Willmar system completed the second stage of development in the fall of 1983. These two new systems demonstrate the benefits of the low-temperature hot water district heating technology. The systems are economical to build, have high reliability, and have low maintenance and operating cost.