This publication provides the basis of the engineering approaches, installation considerations, start-up strategies, and operational strategies for residential heating, cooling, and air conditioning comfort systems and associated accessories. Well designed, properly installed, and properly started and tested space heating and cooling systems and accessories (HVAC) work together to improve the indoor environmental quality (IEQ). These systems tailor comfort to the needs and desires of the occupant and can have a major impact on occupant well-being and health. The energy consumed to condition a home is typically the largest contributor to annual utility costs. Careful attention paid to the selection of total-comfort residential HVAC systems can enhance IEQ at the most economical fi rst and operating costs. A well designed space conditioning system will: a. Maintain space temperature set by the occupants in a narrow comfort range, b. Remove air-borne contaminates, c. Provide clean, fresh ventilation (outdoor) air, d. Control humidity, e. Operate quietly and unobtrusively, and, f. Minimize energy consumption. Today, air conditioners and heat pumps are twice or more as effi cient as similar equipment was 20 years ago. The new generation of condensing furnaces and boilers are approaching 100 percent combustion effi ciency. Include supereffi cient air fi ltration, automatically controlled humidifi ers, and energy effi cient appliances and homes can actually cost less to condition and operate today in spite of signifi cantly higher electric energy and fuel cost.