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Happy earth day everyone! I briefly contemplated a doom and gloom post about the state of the global climate and lack of regulation. But let’s focus on what does work, albeit at a much smaller scale, instead of what doesn’t work.

Team Auffhammer has invested a lot of money in energy efficiency measures in our home. We have new windows ($$$$), a new roof ($$$), German shutters ($$), more efficient appliances ($$) and LED lighting ($) throughout the house. I have been monitoring our energy consumption after each of these investments and could not detect a structural break in our consumption of electricity or natural gas.

Last September I was at the Apple store and saw they sold a “smart” thermostat called the “NEST”. I checked with a genius (they wear blue shirts) and she said that people liked them and they were easy to install and looked cool. I was sold. I went home. Ripped out our old thermostat and put in the new one. Shiny, cool looking and simple. I then did not program it and let it learn our patterns. The thermostat guesses when you are away (with a minimal number of type I and type II errors). Plus, you can control the thermostat from your phone, tablet or the web. So if you leave for vacation and forget to turn it off, you can do so from the beaches of Maui.

I did not think much was going to happen. Boy was I wrong. The picture below displays our electricity consumption for the past 12 months in green and the previous 12 months in red.


The blue dashed line displays the installation date of our thermostat. This is a highly unscientific difference in difference by picture estimate. By using the previous year’s consumption as my counterfactual this picture suggests that we have consumed 1055 fewer kWhs since last September, which is an average savings of 150 kWhs per month or a 22% decrease in consumption.  Wow!

How much did my new fancy thermostat save me? We actually use(d) a fair number of kWhs which cost $0.29, due to the increasing block rate pricing structure (the more you use the higher the price of the next block of kWh consumed). After spending way too much time with my bills, I figured out that I saved almost $210 since September. If my forecast is right I will have made my money back by the end of the next billing cycle.

Now, I would be an irresponsible social scientist by simply prescribing these fancy $249 thermostats for everyone. The NEST changed our behavior. It brought energy conservation to our attention and each member of the family interacts with this shiny gadget a few times a day. We frequently question whether we really need to turn on the AC or heat. Maybe more importantly this thing is fun to use and looks cool.

Now go outside and do something nice for mother earth. And again tomorrow. And the next day. And the day after……..

And no, this blog post was not sponsored by Nest.

Maximilian Auffhammer View All

Maximilian Auffhammer is the George Pardee Professor of International Sustainable Development at the University of California Berkeley. His fields of expertise are environmental and energy economics, with a specific focus on the impacts and regulation of climate change and air pollution.

14 thoughts on “Nest(ing) Leave a comment

  1. I know this is an old post, but out of curiosity, was your old thermostat programmable and did you have it set up to lower your energy usage during times you were typically away from the house?

  2. Max,
    I’m having trouble getting my arms around what exactly happened in your home. The winter electricity savings are too large to come solely from reduced fan operation (an implied reduction of over 250 hours/month!). Also, the pattern of savings doesn’t correlate in any obvious way to seasons.
    My guess is that, yes, the Nest may have contributed to the reduction but a host of other factors (not captured in your counterfactual) are more likely responsible. You identified some of them: behavior, other retrofits, and perhaps even differences in weather. If I had known nothing else than the kWh plot, I would have guessed that you had replaced a 20-year refrigerator with a new model.
    Displaying the gas consumption — the primary target of the Nest’s intellectual firepower — might help disentangle some of the contributing factors.

    – alan

    P.S. Here’s what the smart meter sees when you replace an old guzzling refrigerator

    • Hi Alan:

      I am as shocked as you are. I think the biggest benefits come from “auto-away” or us turning off our HVAC system for extensive periods of time. I see similar savings in natural gas (~13%). We made no other energy efficient investments around the time of the nest. Everything else came way before then!


  3. My problem with Nest is that they seem to be going the Apple route and trying to invent their own world of PCT. They have chosen (so far) to eschew the Zigbee HAN solution that has been deployed with the smart meters (in CA). This prevents them (for now) from participating in any demand response programs that come through the utility. I wonder if they are positioning themselves to be able to capture a demand response market created by Nest users that is not accessible to any other third party aggregator. Anyway, I think they could broaden their impact if they supported the Zigbee HAN.

    • Good question! In our house a giant fan operated by electricity blows the hot air around the house, which is common in California. I see similar savings in percentage terms in our natural gas consumption.mmax

  4. Max,

    Great post–I like hearing stories of what people actually do. Perhaps another time you can plot your gas + electricity, and show when you did all your home retrofits.
    One suggestion on the current plot, label the x-axis as “months” and the y-axis as “kWh/month”. That way the data jockies can play with your data.



  5. Do you think that the device altered your behavior or did it better adapt your HVAC to your “normal” behavior?

    • Hi Mike:

      I think it is a mixture of both. We changed our behavior a bit, yet the Nest decreased the number of times we were heating or cooling an empty house.
      Thanks for reading! Max

  6. A NEST might be the right solution for an existing home. For new homes, the answer is to build it correctly considering ambient conditions. Besides, I’d need 11 NESTS in our home, one for each room that currently has its own thermostat (we have radiant heat).

  7. Hm, I would have expected to see more of a thermostat-upgrade effect in the heating/cooling-intensive months, yet it seems like the smallest effect was in January. I wish you had a plot for the difference in HDD and CDD between those two 12-month periods!

    • Hey Leslie: You are right. should have posted the HDD/CDD adjusted data. PG&E does that for your entire bill and our weather adjusted savings went up significantly after the installation as well. Max

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