The largest amount of house hold energy use in the Us is for space heating and natural gas is the predominant source of this energy. About 20% of the energy use in the us is for space heating. Prior to world war Ii in the 1940s, coal and wood were important sources of home heat Ideal house. perfect thermal insulation in the wall. windows roof and floors and no leakage of air into and out of the house and no radiation energy coming in or going out of the windows Any attempt to approach this ideal is limited in effectiveness by the cost and inconvenience of unreasonable amounts of insulation Nevertheless many well-designed houses have been built that require no separate heating system. They are heated adequately by existing internal sources of heat energy such as lights and cooking stoves 复旦大学环境科学与工程系 Department of Environmental Science and Engineering, Fudan UniversityThe largest amount of house hold energy use in the US is for space heating, and natural gas is the predominant source of this energy. About 20% of the energy use in the US is for space heating. Prior to World War II in the 1940s, coal and wood were important sources of home heat. Ideal house, perfect thermal insulation in the wall, windows, roof, and floors and no leakage of air into and out of the house, and no radiation energy coming in or going out of the windows. …. Any attempt to approach this ideal is limited in effectiveness by the cost and inconvenience of unreasonable amounts of insulation. Nevertheless, many well-designed houses have been built that require no separate heating system. They are heated adequately by existing internal sources of heat energy such as lights and cooking stoves