In the late nineteenth and early twentieth centuries, heating a home was a matter of tossing another log or more coal into the fireplace or stove. "Air conditioning" was the shade of a backyard tree. Twenty-first century homes use far more sophisticated technological tools—tools that a homeowner is likely to take for granted.

A heating and air conditioning contractor has to be as much of a scientist as a builder or technician. The course requirements of typical heating and air conditioning programs at community or junior colleges place a heavy emphasis on chemistry, physics, engineering, and mathematics, including geometry and algebra. Good heating and air conditioning contractors are able to compute formulas and equations in order to arrive at volumes, pressures, and degrees. They must be able to accurately measure distances, angles, circles, arcs, temperatures, weights, and volumes. They also must...