Measured vs Predicted Savings from Single Retrofits

Energy savings from single retrofits in one-and two-unit homes have been investigated in order to provide more reliable estimates to homeowners who are considering a conservation investment. The samples were drawn from households that had financed conservation measures through a city futility loan program. The sample groups studied to date are small, and the results are therefore tentative. Nevertheless, they provide an indication of the level of savings that is actually being achieved by these retrofits.

Installation of high-efficiency furnaces and boilers produced an average savings of 14% of total weather-normalized annual gas use (NAC). These savings average about 80% of the predicted savings based on Minnesota's Residential Conservation Service (RCS) calculations. The median simple payback was 23 years. Wall insulation showed an average savings of 12% of NAC, with a median payback of 12 years. Adding attic insulation to houses where some insulation was present gave small savings that were not statistically different from zero. Actual savings for wall and attic insulation averaged about half of the predicted savings based on RCS calculations.

These preliminary results corroborate our previous findings based on engineering estimates that wall insulation has higher savings and a faster payback than attic reinsulation, and that high-efficiency furnace/boiler installations are cost-effective primarily if the existing heating system needs to be replaced anyway.

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Measured vs Predicted Savings from Single Retrofits