You might have heard about the Nest 'learning' thermostat that was created by one of the original iPod designers. For more information about the Nest, click here.
I received this product as a Christmas gift in late 2012 and installed it in early 2013. I read many positive reviews of the product online but was surprised to find very little quantitative data about its performance, and particularly the energy savings. To provide such information, I have estimated the savings using my own home's energy use in comparable months (February 2012 vs. February 2013).
My utility, Vectren Energy, uses 65 F as the basis for its heating 'degree-day' calculations (for the definition of a degree-day, click here). I was pleased (and a bit surprised) to find that my normalized natural gas usage dropped from 0.25 therm/degree-day to 0.21 therm/degree-day -- a 16% reduction. Of course, some caveats apply. For example, we definitely were keeping the house a bit cooler even when we were awake and at home, but conversely, the other gas appliances (oven/range and water heater) would not be affected by the thermostat.
Given that our gas utility costs have been roughly $1,000 per year, the annual savings from natural gas usage should be about $150. Further, I expect that the savings on electricity this summer with the Nest in charge of the central air conditioning will make the payback time less than a year (i.e., the time at which our utility savings have exactly offset the initial expense, which was approximately $250). I'll provide an update on summer A/C use later this year.
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