Direct heating began with open fires, using wood or charcoal. Chinese invented enclosed stoves around 600 BC. Romans developed hypocaust system using hot gases beneath floors. Central heating reintroduced during Industrial Revolution
Central cooling systems use ductwork to distribute heated or cooled air. Split-system ACs and heat pumps have indoor and outdoor units. Packaged units sit outside, cooling and supplying air through ducts. Cooling process involves evaporator coil absorbing heat and refrigerant. Heat pumps can switch between heating and cooling automatically
Central heating provides warmth to multiple spaces from one main heat source. Systems use furnaces, fans, steam or pumps to circulate heat. Primary energy sources include coal, wood, oil, natural gas or electricity
Central heating provides uniform temperature throughout the house. Systems use fuel to extract thermal energy and transfer it indoors. Thermostat controls temperature and cycles heating system accordingly
Central furnaces distribute warm air through ducts using natural gas, oil, or electricity. Modern furnaces use inducer fans to reduce exhaust heat loss. Boilers heat water, which circulates through radiators and returns to boiler. Heat pumps use forced air or ground-source heating systems
Pellet heating systems available for all output ranges from 10 to 1,000 kW. Small-scale boilers provide central heating and hot water for 10-50 kW systems. Pellet stoves offer space heating and hot water systems with back boilers. Heating stations can power entire complexes with 50-1,000 kW output