District heating (also known as heat networks or teleheating) is a system for distributing heat generated in a centralized location through a system of insulated pipes for residential and commercial heating requirements such as space heating and water heating. The heat is often obtained from a cogeneration plant burning fossil fuels or biomass, but heat-only boiler stations, geothermal heating, heat pumps and central solar heating are also used, as well as heat waste from factories and nuclear power electricity generation. District heating plants can provide higher efficiencies and better pollution control than localized boilers. According to some research, district heating with combined heat and power (CHPDH) is the cheapest method of cutting carbon emissions, and has one of the lowest carbon footprints of all fossil generation plants. Fifth-generation district heat networks do not use combustion on-site and have zero emissions of CO and NO on-site; they employ heat transfer using electricity, which may be generated from renewable energy or from remote fossil-fuelled power stations. A combination of CHP and centralized heat pumps is used in the Stockholm multi-energy system. This allows the production of heat through electricity when there is an abundance of intermittent power production, and cogeneration of electric power and district heating when the availability of intermittent power production is low. District heating is ranked number 27 in Project Drawdown's 100 solutions to global warming. History District heating traces its roots to the hot water-heated baths and greenhouses of the ancient Roman Empire. A hot water distribution system in Chaudes-Aigues in France is generally regarded as the first real district heating system. It used geothermal energy to provide heat for about 30 houses and started operation in the 14th century. The U.S. Naval Academy in Annapolis began steam district heating service in 1853. MIT began coal-fired steam district heating in 1916 when it moved to Cambridge, Massachusetts. Although these and numerous other systems have operated over the centuries, the first commercially successful district heating system was launched in Lockport, New York, in 1877 by American hydraulic engineer Birdsill Holly, considered the founder of modern district heating. Generations of district heating Generally, all modern district heating system are demand driven, meaning that the heat supplier reacts to the demand from the consumers and ensures that there is sufficient temperature and water pressure to deliver the demanded heat to the users. The five generations have defining features that sets them