Maintaining Constant Temperature

The purpose of a heating system is to maintain a constant temperature. To do this, all heating systems—whether it is for heating a small room or a domed stadium—must compensate for heat losses with heat gains. Even though the human body continually loses heat through conduction with the surrounding air and evaporation of water from the surface of the skin, the temperature of the human body is remarkably constant. For every joule of heat flowing from the body, there is one joule produced by mechanisms that convert energy from food. If heat loss quickens (e.g., while one is swimming), the heat regulators in the body convert more energy from food to compensate.

It is the same with a room in a building. Heat is lost through many tiny openings to the outside and through conduction through...