During the first energy crisis of 1972, the Federal Government realized that they would have to look into ways to reduce our dependence on foreign oil. Several research facilities were given grants to study various areas of energy use, and in 1974 a group at Princeton University's Center for Energy and Environmental Studies was given the job of figuring out how houses lose heat.

They spent several years quantifying energy loss and found that they always came up with a "mystery factor" that they couldn't explain. They developed a very complicated, time consuming and expensive method of measuring air leakage from the outside and were able to show that air leakage was a major contributor to energy use. Knowing this, they then developed a very quick method of doing the same thing - a large fan called a blower door that fits temporarily into an exterior door that is used to depressurize the house to test pressures that allow an infiltration rate to be calculated.

After measuring air leakage in many houses and looking at their bills, the team found an additional but smaller variation that they could not explain. They borrowed an infrared scanner from a previous project - working with rocket engines for the NASA lunar project - and found that many interior walls and cavities were cold. An infrared scanner does not look into a wall, but rather it looks at temperatures on the surface of the wall and allows the operator to make judgments about the presence and quality of insulation inside the wall, and the effect that air movement - both infiltrated and convected - is having.

This was the first time that convection was understood to have influence on comfort and bills. Convection is the movement of warm air up and cold air down, and it is distinct from infiltration, although the two are commonly connected. Convection can make the walls around a shower with a dropped ceiling be very cold. Convection can make the floor of the second level of a Cape Cod house be very cold. Convection can make the pipes freeze in a bathroom in the center of a balloon framed farmhouse. These convective problems also came to be known as attic bypasses. Sealing these convective loops reduced bills, increased comfort, and finally made the bills predictable.

The team found that tightening a house against air leakage and sealing convective problems are two of the most cost-effective repairs that can be done to an existing house. If this work can be done to a new house under construction then benefits are actually greater with a smaller cost.

In 1981, the Princeton team put together a package that allowed a contractor to diagnose and repair energy and comfort problems in houses and they called it the Princeton House Doctor Approach.

Also in that year, Energy Services Group became the first commercial business trained and equipped by the original Princeton researchers using their approach, which stresses both the necessity for analysis and measurement of problem areas and the cost-effective repair of those items dictated by analysis.

We are now in our third decade of this important work, and several refinements have been made to the basic approach. Along with the Blower Door to measure and find air leakage and infrared scanners to quantify convection, we have the technology to measure and diagnose problems in furnace efficiency, duct delivery and leakage, humidity, and temperature variations.

In addition, we can help builders to increase the efficiency of their homes by designing in cost-effective measures, and we can offer HERS, home energy ratings, to allow a builder to qualify his homes for several programs such as the EPA's Energy Star program.