The Rockford home had several appliances that were not being used or were being underused.

There were two older, underused refrigerators in the garage. In most households, the refrigerator is the single biggest energy-consuming kitchen appliance. A standard refrigerator will use about 489 kWh per year, compared to 387 kWh for the most energy efficient unit. The typical standard freezer will use about 687 kWh per year, compared to 616 kWh annually for the most energy efficient unit. Older refrigerators are not very energy efficient and are doubly wasteful when underused for secondary storage.

The Rockford home also used an electric clothes dryer, although a natural gas dryer was available. In general, gas dryers cost approximately 40% to 50% less annually to operate than electric dryers.

To increase the energy efficiency of the home, the two garage refrigerators and freezer were disconnected and removed, with their contents transferred to the main refrigerator in the house. The natural gas dryer was connected and the electric dryer removed.

Estimated Energy Savings

Removing the electric dryer and hooking up the natural gas dryer contributed a 0.6% annual savings (879 kWh or $79) while increasing gas consumption slightly (30 therms or $31). Removing the two refrigerators from the garage added an additional 1.4% annual energy savings (2,080 kWh or $187). The total electric savings for these two measures was 2,959 kWh or $266, at electricity price of $0.105/kwh. 

However, when all five energy-savings measures were carried out together, the result was an annual estimated energy savings of 35% (a combined 5,010 kWh and 1,664 therms). This translated into a net $450 electric and $1,814 natural gas savings, or a total of $2,264/year at energy prices of $0.105/kwh and $1.09 per therm.

The total savings is not the sum of all the individual measures because of interactions between the measures. For example, replacing incandescent lights with compact fluorescent lights saves electric energy but, because the compact fluorescent light gives off less heat, winter heating bills may increase somewhat. As the number of measures increases, these interactions become more complex.