FAYETTEVILLE, Ark. (June 23, 2009) -- Initial results from a research study in East Tennessee show that energy-efficient upgrades can pay off by reducing heating costs by 35 to 65 percent. The study uses three similar homes in the same development to gather real-world data about various energy-efficient improvements that can be made to an existing home.

While the study focuses on improvements to existing homes, new unoccupied homes were used to keep the results as unbiased as possible. The houses are typical two-story models built on insulated slabs with similar solar orientation, lot slope, wall areas, wind exposure and size. Computers and instrumentation are programmed to simulate occupancy, including opening refrigerator doors, automatic clothes washing and drying, showers, lights and plug loads in all three homes. But that’s where the similarities end.

The control or builder home was built to meet current building codes and earned a Home Energy Rating System score of 90, slightly better than a typical code-compliant home. It is equipped with two heat pumps, one for each floor, that have a total capacity of 4.5 tons.

The retrofit house includes energy-efficient upgrades that focus on the building envelope and mechanical equipment. These allowed the HVAC system to be reduced to one, three-ton heat pump located inside the conditioned envelope. The retrofit home earned a HERS rating of 66 – a better score than the builder’s home.

“The retrofit unit provided 35 percent measured heating energy savings from the builder home, yet offers a package of technologies that are considered to be a reasonable upgrade for many homes in the United States,” said Jeff Christian, a senior researcher in the Department of Energy’s Oak Ridge National Laboratory.

Improvements to the home include installing low-E gas-filled windows, changing all light bulbs to compact fluorescents, and replacing the ceiling insulation with spray polyurethane foam insulation on the underside of the roof deck and attic walls to make it an unvented, semi-conditioned space.

“An unvented attic is particularly helpful in climates where heating and cooling equipment is located in the attic,” said Chris Porter, building science manager for BioBased Insulation. “Modifying the attic to create an indirectly conditioned space helps significantly reduce energy consumption and improves mechanical equipment performance.”