In a 100 percent WWS world, air and water heating and air conditioning in buildings will be provided either by district heating and cooling systems or by individual heating and cooling systems. In both cases, heating and cooling will be provided primarily by electric heat pumps, where the electricity comes from WWS sources and the heat or cold is extracted from the air, ground, water, or a waste stream of hot or cold air or water. The heat and cold may be stored or used immediately. Additional heat may come from geothermal and solar heat. The remaining energy used in buildings is for electric appliances and gadgets, such as lights, televisions, computers, and phone chargers. This chapter discusses how WWS will power district and individual-building heating and cooling systems, including hot and cold storage options for both. It also discusses electric appliances and machines that will replace natural gas ones in buildings and their gardens. The chapter also examines energy efficiency in buildings and techniques to reduce building energy use. Finally, it discusses a modern district heating and cooling system and an all-electric home.