Heating has had a major impact on human development by allowing people to reside and function far from the temperate areas of the earth. Heat warms human beings in one of three ways--conduction, convection, or radiation.

Conducted heat passes directly from a heated object into the body, as with the heated bricks and warming pans which chased the chill from beds in Colonial times, or modern-day electric blankets and battery-operated socks. Convection, the main principle in forced-air furnaces, heats the air around the body. The third type, radiation, resembles the warmth of the sun in that heat moves outward in waves and maintains an even temperature. Radiation heat is commonly found in electric coil bathroom wall heaters and quartz space heaters for porches and patios.

The most primitive heating systems were cave fireplaces, which early people improved upon by cutting draft holes to allow smoke to escape. Native...