The Nest Thermostat and Heating Costs

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The short version: I highly recommend the Nest learning thermostat, particularly for a multi-zoned house.

We have three zones: living room, bedrooms, and another for the rest of the house. (Perhaps arguably four zones, since I use a space heater in my office — no reason to heat the whole house when only my office needs to be heated during the week.) When we bought the house, all three thermostats were cheap non-programmable ones; I considered upgrading to programmable thermostats essential, though the cost and features of the Nest were certainly a luxury. I purchased and installed a Nest (second generation) in the living room, and after just a few weeks of seeing both how well it worked and how informative it was, I purchased two more (also second generation) for the other two zones. The Nest proved that the features it offers weren’t just luxuries — more details below.

Installation of the Nest is easy. The programmability is great — it’s very intuitive, easy to use, and navigate. Making adjustments through the iOS app or website is even easier. We can’t use some of the capabilities, such as fan control, because we don’t have central heating. The monthly energy report is nice, too. But the feature that really makes it fantastic is the daily energy report. Not only does the daily energy report show how much energy is used (in our case, how much oil is burned), but it shows a breakdown of when the heat turned on and off. A daily report of our living room is the lead image, above.

In other words, the Nest is telling me exactly how much oil we used to heat the house yesterday, and with three zones I know exactly where that heat is going. Different schedules in each of those zones let me very easily get a feeling for how efficient the heat is working.

2015

In the beginning of 2015 I set out to better weather-seal the house. Primarily, replacing foam insulation around door frames and putting plastic over the windows that had an obvious draft, as well as plastic over the door to the attic. We could tell an immediate improvement to heating efficiency: we could feel the warmth. Our tank of heating oil lasted quite a bit longer — had I tracked the number of days I bet I could have figured out how much of an improvement there was to efficiency. I didn’t need to, though: by looking at Nest’s daily reports I was able to see a 25-30% decrease in the daily energy use to heat the whole house. A huge savings! Most of that came through sealing out the cold in the living room, where the majority of the heat was lost. I didn’t record more specific numbers than that, however.

The Nest was instrumental in helping me improve the efficiency because I could make changes and then see the next day’s heating report to understand how my change impacted energy use. As I said, the living room is where the majority of heat was lost. One of the windows had a terrible draft that I used plastic to seal. The other windows didn’t seem to have any draft but a lot of cold could be felt against the other windows. I suspected that the nine large windows were making convection cooling into a bigger problem, and adding plastic to those windows offered a little bit of insulation for us to see energy savings of a few more percent. We couldn’t feel a difference but the Nest was reporting that we used about 10% less energy in the living room.

2016

This year, I’m looking more critically at the data from the Nest about each of our zones. Thanks to Nest daily reports I see that:

  • About 26% of our heating oil goes to heat the “rest of the house”: kitchen, dining room, and our offices. I’m quite pleased with this. I think I see a few areas we can improve this, but overall it is very efficient.

  • About 37% of our heating oil goes to heat the living room. This might sound bad at first, but I think it’s reasonable given the size of the living room. Our living room measures 20- x 28-foot, or 560 square feet. The ceiling is very high and vaulted, however, so cubic feet is a more accurate measurement. With an 8’ ceiling that would be 4,480 cubic feet, however ours measures 8,310 cubic feet — nearly double!

  • About 37% of our heating oil goes to heat our bedrooms. The thermostat is in the master bedroom, so this is an accurate description of only that room. Their’s a master bath that is also heated and the thermostat is effectively reading that, too, since that door is typically open. The master bedroom measures 11- x 15-foot and the bathroom measures 7-1/2- x 5-foot, for a total of 202.5 square feet. (It has 8’ ceilings, too, so that’s about 1,620 cubic feet.) Thinking about cubic footage, the living room is more than five times larger than the bedroom, yet it’s using the same amount of energy to heat! Clearly there is a problem here. I haven’t been able to locate any particularly troublesome spots with an infrared thermometer; I think I’ll have to rent a thermal camera to get a better understanding of what may be going wrong.

We have a wood stove in the living room and have started using it. With a supply of downed trees on our property for firewood, it’s essentially free heat. Using a fire to supplement the oil heat, we can cut the living room daily energy use by about half. Cutting the oil use in the living room by that much equates to about a 20% reduction in our total heating oil costs. We haven’t burned enough wood to say if it might be worth paying for wood in the future, but I suspect not. As long as we can get it for free it’s worthwhile, though!

Summary

Between the savings measured in 2015 energy usage and now the savings realized in using the wood stove in 2016, the daily cost of heating our house has decreased to as much as 56% of what it originally was. (Though only occasionally burning wood in the stove means that number is going to be higher, depending upon how much we burn, perhaps up to about 65% of what it originally was.)

As I wrote I need to look into the bedroom heating and insulation to decrease the energy usage there, and I’m hopeful we can make significant improvements to save even more on heating costs.

The Nest is expensive at $250, and we bought three of them (total: $750). I estimate that, so far, the Nest has let us save about $600 in heating oil costs. By the end of this winter the Nest thermostats will have completely paid for themselves.

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