The Stockton project, a two-year analysis of four homes of varying age in Stockton, Calif., is being used to compare the efficacy and value of various energy retrofit components. One of the findings is that HVAC ductwork in attics makes the cooling systems in the homes use 1.5 to 2.4 times the amount of energy compared to ductwork hung in the conditioned space. After attic insulation was added above the ductwork, and other efficiency measures — including high-performance windows and wall insulation on the two oldest homes — were taken, researchers saw cooling power efficiency gains from 35 to 74 percent.
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