Does the Nest Learning Thermostat Save Energy?
The Nest Learning Thermostat has been on the market for nearly four years now. One of the biggest things the Nest folks use as a selling point is energy savings. “Programs itself. Then pays for itself.” That’s the first thing you see when you go to the Nest homepage. But what do the data say? Three independent studies plus a whitepaper from Nest provide some answers.
The Nest Learning Thermostat has been on the market for nearly four years now. One of the biggest things the Nest folks use as a selling point is energy savings. “Programs itself. Then pays for itself.” That’s the first thing you see when you go to the Nest homepage. But what do the data say? Three independent studies plus a whitepaper from Nest provide some answers.
The first study was done on 185 Oregon homes that used heat pumps, and the study was conducted over one heating season (2013-14), with the report released in October 2014. Two nearly identical studies run by two different gas and electric utilities in Indiana looked at both heating and cooling in a total of 700 homes. The results were nearly identical, too. Finally, Nest published a whitepaper in which they analyzed the energy use of 735 Nest owners with gas furnaces and 624 Nest owners with electric cooling. (See links to all studies at end of article.)
Let’s take a look.
A study in Oregon
This one was focused on heating with heat pumps. The goal was to find a way to reduce the amount of electric resistance heat that typically is installed as a supplemental heat source in heat pumps. The Energy Trust of Oregon, which launched the research project, was looking for an alternative to their “advanced heat pump controls measure.” As I showed in my recent article on Michael Blasnik’s presentation on big data from Nest, there’s a lot of opportunity for savings in heat pump supplemental heating.
The Energy Trust installed the Nest thermostats in 185 homes, and 174 of those made it all the way through the study with the thermostat installed and working. The researchers looked at energy use in the heating season before and the heating season after installation of the Nest. They also interviewed the participants at the end of the study period.
Here what I think are two of the biggest results they found when they looked at the final data:
- Homes averaged 12% savings of electricity used for heating after installing the Nest. (These numbers have been adjusted for weather.)
- More than 60% of the participants found their homes “somewhat more comfortable” or “much more comfortable” while using the Nest thermostat.
Then there were some interesting things that fell out when they analyzed the data in other ways. They looked at all kinds of demographics — age, education level, housing type, geographic location, and much more — and here are a few that struck me as noteworthy.
- Manufactured homes had the highest savings, almost twice as much as the overall average.
- In homes where the Nest replaced a programmable thermostat, the savings were about twice as high as in homes where it replaced a non-programmable thermostat. The uncertainties were high enough, though, that the report says those numbers only “suggest” that the Nest does better when replacing a programmable thermostat.
- The homes that used the most energy saved the most energy (1,785 kWh per year), whereas the group with the lowest incomes had the highest percent savings: 11.1% (1,654 kWh).
Although the results are encouraging, the Oregon report urges some caution:
We have some reservations about the reliability of the results from the subgroup analyses. Each subgroup comparison began with a relatively small sample of pilot homes and cut it into even smaller pieces to analyze. With such small samples to work with and so many comparisons that the team was interested in, there may have been random fluctuations in the data that resulted in observing spurious differences.
In other words, they feel more confident about the numbers based on all the participants, less so about the ones based on things like those who live in manufactured housing, those who used to have a different programmable thermostat, and those who floss religiously on Sunday, Tuesday, Thursday, and Saturday every single week. Also, the data cover only one heating season, so running it for multiple years would provide a better picture of what’s happening.
Still, one of the biggest takeaways here is that this study found good savings with the Nest thermostat connected to heat pumps. In their whitepaper, Nest discussed the difficulties of using setbacks with heat pumps and included a US Department of Energy warning: “Programmable thermostats are generally not recommended for heat pumps.” That’s because many of them tend to cause the electric resistance heat to run more as the heat pump attempts to recover from setbacks.
Two studies in Indiana
These two projects were done by two different gas & electric utilities in Indiana. The Cadmus Group conducted both studies and wrote the reports. Both studies looked at gas use during heating season and electricity use during cooling season. One of the studies had 400 participating homes, the other 300.
The Oregon project was a pre- and post-installation study with the same group of homes. The Indiana studies were different. They compared the energy use in homes with a Nest thermostat to homes with a standard programmable thermostat (the Honeywell TH211) by looking at each relative to homes with non-programmable thermostats as the baseline.
Here are the main results from both studies:
- For heating, the Nest showed ~13% energy savings compared to the baseline homes.
- For heating, the programmable thermostat showed 8% and 5% savings compared to the baseline.
- For cooling, the Nest showed 16% and 14% energy savings compared to the baseline homes.
- For cooling, the programmable thermostat showed 15% and 13% savings compared to the baseline.
The Nest beat the baseline homes (non-programmable thermostat) by double digits for both heating and cooling. It also beat the standard programmable thermostat for heating. For cooling, the Nest and the programmable thermostat came out about the same.
A whitepaper from Nest
This whitepaper is a good read even without the energy savings information because they discuss a lot of the issues around trying to determine whether or not a given measure saves energy and how you would go about determining the amount of savings. (Read the Background and Methodology sections.)
The Nest energy savings analysis is different from both the Oregon and the Indiana studies. They used “pooled” data from a control group of non-Nest users and compared to data from the Nest users. Both the control group and the Nest users are people who had been using the MyEnergy, a company that “helps customers track and analyze their utility usage and bills.” (Nest bought MyEnergy in 2013.) The chart below shows percent savings for the control group. Notice that the center of the data is at 0% savings.
In contrast to the control group, the data from the Nest users are shifted to the right of the 0% savings line.
The actual numbers they found for savings of natural gas for heating and electricity for cooling are:
- 9.6% for heating (as a percentage of heating, not total energy use)
- 17.5% for cooling (as a percentage of cooling, not total energy use)
The heating number is lower than the other studies, but the cooling number is about the same.
The Nest whitepaper discusses potential biases and the issues surrounding using data from the MyEnergy customers. In the end, though, they conclude that there wasn’t any large bias in the results.
Yes, the Nest does save energy
The results here provide a lot of evidence that the Nest Learning Thermostat does indeed save energy. It saves on heating energy with both gas furnaces and heat pumps, and it saves on cooling with air conditioners and heat pumps. All four of the reports go into the details of their methodology, telling how they chose the participants, how they collected and analyzed the data, and more. (Use the links below to download the papers.)
One important thing to point out here is that the Oregon and Indiana studies used carefully chosen participants, and they installed the Nest thermostats for them. One question that comes up with Nest data sometimes is, what is the effect of having self-selected gadget-geeks or energy savers on the savings data? In those three studies, that’s a moot point. It seems that the average Nest owner will save energy even when they’re not the kind of people who would go out and buy one on their own.
Of course, not everyone buys a Nest because it saves energy. Some people get them just so they can adjust the thermostat remotely from the app on their phone. Maybe it’s even because it’s flossing day, and they have to get up early.
The Four Reports
Oregon Study (pdf)
Indiana Study – NIPSCo (pdf)
Nest Whitepaper (pdf)
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If You Think Thermostat Setbacks Don’t Save Energy, You’re Wrong!
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Does the Nest controls
Does the Nest controls humidity and ventilation as well?
I’d like to see a study where
I’d like to see a study where Time of Use electric rates are present. TOU rate structures are rapidly becoming more common on a national level.
Yes. Nest saves energy. &
Yes. Nest saves energy. <br /> <br />We install Nest, Ecobee 3 and even Honeywell WiFi, but as it is with all HVAC equipment, application matters. <br /> <br />First we assess the clients goals e.g. economy of operation, comfort, smart phone control or alerts, then the system compatibility. Once we find the right thermostat matching system and client we proceed with a rational setup and predict outcomes from experience. <br /> <br />We spend as much time on DIY "troubleshooting" as we do on new installations. <br /> <br />I personally have all three in my office and home.
I have read the Oregon study
I have read the Oregon study closely, and found the case for energy savings with Heat Pumps a little less compelling. <br /> <br />I had a nest on my heat pump for 2 years, and got rid of it b/c it was calling aux way **more** than any other stat I have used, no matter how it was adjusted. So I was interested in seeing this ‘proof’ that nest saves energy with HPs. <br /> <br />The report details that heating energy usage was not tracked separately….it shows that electricity usage was reduced by 5±3% (90% CI) in the study group, and they then assumed that all elec reductions were due to reduced heating energy, and multiplied the 5% by 2.5x. So the estimate is 12±8%. <br /> <br />These numbers were 7±4% of elec in the half the study group in Portland Metro, and 2±6% for the rest of the group in rural locations. I.e. no evidence of savings outside Portland. <br /> <br />I looked up the ave January low in Portland…36°F…which is pretty mild. The other rural locations are at higher altitude and I think prob have cooler weather. <br /> <br />The oregon study also reported that 5-7% of nest thermostats failed and needed replacement, and that one of them in the study group killed the compressor when it did so! NEst doesn’t advertise that on its site. <br /> <br />My problems with the nest were that my defrost cycling caused a small dip in temps that caused the nest on ‘Heat Pump Balance’ mode to call aux. Like every hour, even when it wasn’t needed. When I turned off the ‘smart’ mode, and tried to lock out the aux, I found the min aux lockout temp was 35°F (!!). So, I basically had no way to lock out the aux, except telling the nest I lived in Key West (so it thought it was warm outside). <br /> <br />My hypothesis is that Nest uses MORE aux than other stats in many systems, but only for temps below 35-40°F. The Oregon study does not refute this hypothesis. <br /> <br />They have huge amounts of data from their MyEnergy acquistion on energy usage before and after nest purchases, but have not reported their own anaylsis from HP users. Why not? They have analyzed other types of heating systems. <br /> <br />I would be very happy to have Blasnik report Nest Data for HPs where it at least gets below freezing. <br />
I installed the (DIY)
I installed the (DIY) Honywell Wifi p/n RTH8580WF in my cabin located in Minnesota. I like the ability to turn the heat up or AC on before I arrive with my smart phone. <br />What I do not like about the Honeywell is, it only allows a +/-1 degree before the furnace/AC is turned on and I believe the added cycles is harder on the furnace/AC than any energy savings I am gaining. <br />In my application at the cabin I don’t care about a learning type of thermostat like the Nest, because I am not at the property enough for it to learn my behavior. <br />I believe the NEST cycles +/-2 or 3 degrees, which is easier on my furnace/AC unit and in the summer months would remove more humidity from the building. <br />What is your opinion, should I spend the money on the NEST and replace the 1 year old Honeywell thermostat?
Does the Nest controls
Does the Nest controls humidity and ventilation as well?
Adaptive recovery thermostats
Adaptive recovery thermostats for heating with heat pumps have been around for some time and are usually recommended to clients (several different brands). They slowly increase the "call for heat" temps until the desired high temp is achieved so the aux heat strips do not turn on. It looks to me that the Nest does a more accurate job of providing "programmed temperatures" than the occupants can (with either manual or programmed thermostats). Is this further proof that occupants should not be allowed to <br />"fiddle" with HVAC controls?
I’d like to see a study where
I’d like to see a study where Time of Use electric rates are present. TOU rate structures are rapidly becoming more common on a national level.
Interesting. I appreciate
Interesting. I appreciate Nest’s ability to identify occupancy through sensors and Wifi. However I wish their whitepaper had specified the configuration changes from default. My hot button item is Aux Strip Electric heat, well known to cause huge bills when heat pumps fail. For example single residences sometimes have monthly charges exceeding $750 in Texas when the heat pump failed. The biggest issues I routinely see are heat pumps not cleaned, ducted or charged properly while system failures lead to automatic or manual electric strip usage, typically unknown to the resident until the electric bill arrives. <br /> <br />The only solid reference to the Nest’s Aux Heat Control configuration is in the whitepaper’s page 12 table where it is noted that more savings are available when someone sets "heat pump balance to max savings" rather than "max comfort", which apparently is the default. Meanwhile the referenced Oregon study mentions the thermostat’s “Heat Pump Balance feature as a key element in providing the savings". Assuming it’s on and the heat pump has been installed and maintained optimally to avoid usage of the Aux heat strips, perhaps it does work.
Yes. Nest saves energy. &
Yes. Nest saves energy.
We install Nest, Ecobee 3 and even Honeywell WiFi, but as it is with all HVAC equipment, application matters.
First we assess the clients goals e.g. economy of operation, comfort, smart phone control or alerts, then the system compatibility. Once we find the right thermostat matching system and client we proceed with a rational setup and predict outcomes from experience.
We spend as much time on DIY “troubleshooting” as we do on new installations.
I personally have all three in my office and home.
Test comment
Test comment
I have read the Oregon study
I have read the Oregon study closely, and found the case for energy savings with Heat Pumps a little less compelling.
I had a nest on my heat pump for 2 years, and got rid of it b/c it was calling aux way **more** than any other stat I have used, no matter how it was adjusted. So I was interested in seeing this ‘proof’ that nest saves energy with HPs.
The report details that heating energy usage was not tracked separately….it shows that electricity usage was reduced by 5±3% (90% CI) in the study group, and they then assumed that all elec reductions were due to reduced heating energy, and multiplied the 5% by 2.5x. So the estimate is 12±8%.
These numbers were 7±4% of elec in the half the study group in Portland Metro, and 2±6% for the rest of the group in rural locations. I.e. no evidence of savings outside Portland.
I looked up the ave January low in Portland…36°F…which is pretty mild. The other rural locations are at higher altitude and I think prob have cooler weather.
The oregon study also reported that 5-7% of nest thermostats failed and needed replacement, and that one of them in the study group killed the compressor when it did so! NEst doesn’t advertise that on its site.
My problems with the nest were that my defrost cycling caused a small dip in temps that caused the nest on ‘Heat Pump Balance’ mode to call aux. Like every hour, even when it wasn’t needed. When I turned off the ‘smart’ mode, and tried to lock out the aux, I found the min aux lockout temp was 35°F (!!). So, I basically had no way to lock out the aux, except telling the nest I lived in Key West (so it thought it was warm outside).
My hypothesis is that Nest uses MORE aux than other stats in many systems, but only for temps below 35-40°F. The Oregon study does not refute this hypothesis.
They have huge amounts of data from their MyEnergy acquistion on energy usage before and after nest purchases, but have not reported their own anaylsis from HP users. Why not? They have analyzed other types of heating systems.
I would be very happy to have Blasnik report Nest Data for HPs where it at least gets below freezing.
I installed the (DIY)
I installed the (DIY) Honywell Wifi p/n RTH8580WF in my cabin located in Minnesota. I like the ability to turn the heat up or AC on before I arrive with my smart phone.
What I do not like about the Honeywell is, it only allows a +/-1 degree before the furnace/AC is turned on and I believe the added cycles is harder on the furnace/AC than any energy savings I am gaining.
In my application at the cabin I don’t care about a learning type of thermostat like the Nest, because I am not at the property enough for it to learn my behavior.
I believe the NEST cycles +/-2 or 3 degrees, which is easier on my furnace/AC unit and in the summer months would remove more humidity from the building.
What is your opinion, should I spend the money on the NEST and replace the 1 year old Honeywell thermostat?
Adaptive recovery thermostats
Adaptive recovery thermostats for heating with heat pumps have been around for some time and are usually recommended to clients (several different brands). They slowly increase the “call for heat” temps until the desired high temp is achieved so the aux heat strips do not turn on. It looks to me that the Nest does a more accurate job of providing “programmed temperatures” than the occupants can (with either manual or programmed thermostats). Is this further proof that occupants should not be allowed to
“fiddle” with HVAC controls?
Interesting. I appreciate
Interesting. I appreciate Nest’s ability to identify occupancy through sensors and Wifi. However I wish their whitepaper had specified the configuration changes from default. My hot button item is Aux Strip Electric heat, well known to cause huge bills when heat pumps fail. For example single residences sometimes have monthly charges exceeding $750 in Texas when the heat pump failed. The biggest issues I routinely see are heat pumps not cleaned, ducted or charged properly while system failures lead to automatic or manual electric strip usage, typically unknown to the resident until the electric bill arrives.
The only solid reference to the Nest’s Aux Heat Control configuration is in the whitepaper’s page 12 table where it is noted that more savings are available when someone sets “heat pump balance to max savings” rather than “max comfort”, which apparently is the default. Meanwhile the referenced Oregon study mentions the thermostat’s “Heat Pump Balance feature as a key element in providing the savings”. Assuming it’s on and the heat pump has been installed and maintained optimally to avoid usage of the Aux heat strips, perhaps it does work.
Test comment
Test comment
A properly sized HVAC
A properly sized HVAC appliance is the most important aspect of efficiency and comfort. The ambient temperature differential is the one of the lesser factors in system cycling. Most smart stats will allow for adjustment but each system and user is different. No one setting will work for everyone in every climate, on every system. <br /> <br />
@ Richard Parker,
@ Richard Parker, <br /> <br />Heat Pump Balance is a routine that tries to automatically determine a suitable aux lockout temperature (so the user doesn’t have to). It doesn’t work very well. If the nest finds that there is an indoor temp undershoot, it seems to conclude that the aux lockout temp should be greater than or equal to the current outside temp. In my case, normal defrost cycles at 35°F triggered a tiny drop in indoor temp (~1°F), which even on ‘Max Savings’ caused the nest to fire aux and set the aux lockout temp to 35°F. <br /> <br />My actual balance point is closer to 22°F. <br /> <br />OF course, you can turn ‘Heat Pump Balance’ off, and set an aux lockout manually. Unfortunately, the nest does not allow the manual setting of a lockout temp below 35°F. This appears to be a simple design flaw. I suspect that this number was made up by an intern writing code in LA in 2009, who wasn’t really clear on what aux was, and nobody ever got around to changing it. Maybe they were afraid of freezing houses if the HP failed in cold weather, due to aux lockout. Who knows? <br /> <br />After two years of user feedback on the company forum re the lockout problem/bug from dozens of customers, and tales of multiple fried compressors due to FET failueres on the Nest, no one at Nest Labs appeared even aware that there was a problem with Heat Pumps.
A properly sized HVAC
A properly sized HVAC appliance is the most important aspect of efficiency and comfort. The ambient temperature differential is the one of the lesser factors in system cycling. Most smart stats will allow for adjustment but each system and user is different. No one setting will work for everyone in every climate, on every system.
@ Richard Parker,
@ Richard Parker,
Heat Pump Balance is a routine that tries to automatically determine a suitable aux lockout temperature (so the user doesn’t have to). It doesn’t work very well. If the nest finds that there is an indoor temp undershoot, it seems to conclude that the aux lockout temp should be greater than or equal to the current outside temp. In my case, normal defrost cycles at 35°F triggered a tiny drop in indoor temp (~1°F), which even on ‘Max Savings’ caused the nest to fire aux and set the aux lockout temp to 35°F.
My actual balance point is closer to 22°F.
OF course, you can turn ‘Heat Pump Balance’ off, and set an aux lockout manually. Unfortunately, the nest does not allow the manual setting of a lockout temp below 35°F. This appears to be a simple design flaw. I suspect that this number was made up by an intern writing code in LA in 2009, who wasn’t really clear on what aux was, and nobody ever got around to changing it. Maybe they were afraid of freezing houses if the HP failed in cold weather, due to aux lockout. Who knows?
After two years of user feedback on the company forum re the lockout problem/bug from dozens of customers, and tales of multiple fried compressors due to FET failueres on the Nest, no one at Nest Labs appeared even aware that there was a problem with Heat Pumps.
We’ve been using an air
We’ve been using an air source heat pump for 14 years. The things I’ve learned for the most efficient heating operation are: lock out electric heat strips during defrost calls, lock out auxiliary strip heat to the lowest possible setting (5F for our Carrier unit) that will maintain the desired indoor temps., stage the programmable thermostat (carrier model) for gradual increases in temperature during very cold conditions when capacity is limited, and use the "always on" low speed fan to prevent air stratification. <br /> <br />The balance point in our 1982 split level home in S. Indiana is between -5F and 0F with our 2.5 ton, HSPF 8.5 air source heat pump. Our heating demand this past winter for the coldest month was around 9K Btu/hr from energy analysis. Even though our heat pump is cooling oversized, it does provide enough heating capacity for the coldest month here with little to no electric heat strip use. <br /> <br />Maybe Nest employees should install heat pumps in their homes and use them?
We’ve been using an air
We’ve been using an air source heat pump for 14 years. The things I’ve learned for the most efficient heating operation are: lock out electric heat strips during defrost calls, lock out auxiliary strip heat to the lowest possible setting (5F for our Carrier unit) that will maintain the desired indoor temps., stage the programmable thermostat (carrier model) for gradual increases in temperature during very cold conditions when capacity is limited, and use the “always on” low speed fan to prevent air stratification.
The balance point in our 1982 split level home in S. Indiana is between -5F and 0F with our 2.5 ton, HSPF 8.5 air source heat pump. Our heating demand this past winter for the coldest month was around 9K Btu/hr from energy analysis. Even though our heat pump is cooling oversized, it does provide enough heating capacity for the coldest month here with little to no electric heat strip use.
Maybe Nest employees should install heat pumps in their homes and use them?
Interesting that AUX heat use
Interesting that AUX heat use is a big discussion n here. 75% of all electric homes in Oklahoma are 100% resistance heat, straight cool units. A few home-owners are starting to understand how much cheaper heat pumps are, but it’s an uphill battle when power is only 6 cents per KWH.
Interesting that AUX heat use
Interesting that AUX heat use is a big discussion n here. 75% of all electric homes in Oklahoma are 100% resistance heat, straight cool units. A few home-owners are starting to understand how much cheaper heat pumps are, but it’s an uphill battle when power is only 6 cents per KWH.
In my opinion it's
In my opinion it's not even really worth discussing the technical merits of the Nest in the context of the evidence provided. The study does not provide good evidence that the Nest saves energy, it provides very weak evidence. The comparison group is totally uncontrolled in the Oregon study, whereas those receiving the Nest did so based on specific criteria (see page 3-3). In addition, the comparison group didn't receive any intervention, nor were they contacted for the study. This is not a control group. If the Nest thermostat were a medical intervention, it's unlikely that anyone would have sought FDA approval for it based on this study. This is because medical researchers understand placebos and control groups.
This is not trivial. Understand, the people receiving the Nest had to be motivated enough to allow for a large intervention. The comparison group did not. This makes those receiving the Nest thermostat very different from the comparison group.
In my opinion it's
In my opinion it's not even really worth discussing the technical merits of the Nest in the context of the evidence provided. The study does not provide good evidence that the Nest saves energy, it provides very weak evidence. The comparison group is totally uncontrolled in the Oregon study, whereas those receiving the Nest did so based on specific criteria (see page 3-3). In addition, the comparison group didn't receive any intervention, nor were they contacted for the study. This is not a control group. If the Nest thermostat were a medical intervention, it's unlikely that anyone would have sought FDA approval for it based on this study. This is because medical researchers understand placebos and control groups.
This is not trivial. Understand, the people receiving the Nest had to be motivated enough to allow for a large intervention. The comparison group did not. This makes those receiving the Nest thermostat very different from the comparison group.
How about listing the SEER /
How about listing the SEER / EER ratings of the equipment that the nest is attached too?
It kind of counter productive to say wow! I’m saving $3 a month by installing a Nest for my 10 SEER AC unit. When in most cases of my market replacing the 10 SEER AC system results in average savings of around $100 month or more… depending on the system chosen and the SEER rating of the unit you are replacing.
You can go a step further to save money and become more comfortable by installing a zone system. I have listed all my energy bills since around 2010… my average cost for AC usage is usually less than $35 a month and I live in Katy, Texas (a suburb of Houston).
Often people pick the gimmick based approaches to solve problems and then wonder why the results aren’t really much to speak of.
Twenty years in the field of HVAC service, repair and installations I have seen just about every scenario under the sun.
Never forget the "service after the sale" aspect… because
in the recent heat we’ve had there is no equipment on this planet immune to breaking down.
Stay cool my friends and more importantly stop over paying the utility company for it.
How about listing the SEER /
How about listing the SEER / EER ratings of the equipment that the nest is attached too?
It kind of counter productive to say wow! I’m saving $3 a month by installing a Nest for my 10 SEER AC unit. When in most cases of my market replacing the 10 SEER AC system results in average savings of around $100 month or more… depending on the system chosen and the SEER rating of the unit you are replacing.
You can go a step further to save money and become more comfortable by installing a zone system. I have listed all my energy bills since around 2010… my average cost for AC usage is usually less than $35 a month and I live in Katy, Texas (a suburb of Houston).
Often people pick the gimmick based approaches to solve problems and then wonder why the results aren’t really much to speak of.
Twenty years in the field of HVAC service, repair and installations I have seen just about every scenario under the sun.
Never forget the “service after the sale” aspect… because
in the recent heat we’ve had there is no equipment on this planet immune to breaking down.
Stay cool my friends and more importantly stop over paying the utility company for it.
$35/mo for AC? How big is the
$35/mo for AC? How big is the house? How much total KWH use in summer? SEER and size of AC?
$35/mo for AC? How big is the
$35/mo for AC? How big is the house? How much total KWH use in summer? SEER and size of AC?
None of those studies have
None of those studies have proven that Nest saves energy. Most studies shown here are completely biased and thus useless to reach any conclusion. The main problem for the studies is that people that buy a Nest would be most interested in saving money and therefore would pay more attention updating the thermostat to their needs. Therefore, those motivated people would save money after spending money in ANY thermostat. Why the studies are all invalid? They should have been 1) randomized (otherwise as said, people who voluntarily buy a Nest or any other would most likely save money anyway), 2) use positive and negative controls (only the study in Indiana did), 3) ideally blinded (meaning that the devices are masked through another device so that participants do not know which thermostat are using (not sure if possible though). The only study decently design (Indiana) did not confirm that Nest saves more than a regular thermostat; with definitely no difference in cooling and a marginal better performance in heating but still in the "unconfirmed" range (increase that was not statistically significant i.e. it could not be real, just by chance). Bottom line is that most people saves money after buying a new thermostat because they are motivated (specially after spending several hundred dollars.. It must be worthy), paying a lot more attention in programming it accurately to their needs. That happens with ANY thermostat, including but limited to Nest.
None of those studies have
None of those studies have proven that Nest saves energy. Most studies shown here are completely biased and thus useless to reach any conclusion. The main problem for the studies is that people that buy a Nest would be most interested in saving money and therefore would pay more attention updating the thermostat to their needs. Therefore, those motivated people would save money after spending money in ANY thermostat. Why the studies are all invalid? They should have been 1) randomized (otherwise as said, people who voluntarily buy a Nest or any other would most likely save money anyway), 2) use positive and negative controls (only the study in Indiana did), 3) ideally blinded (meaning that the devices are masked through another device so that participants do not know which thermostat are using (not sure if possible though). The only study decently design (Indiana) did not confirm that Nest saves more than a regular thermostat; with definitely no difference in cooling and a marginal better performance in heating but still in the “unconfirmed” range (increase that was not statistically significant i.e. it could not be real, just by chance). Bottom line is that most people saves money after buying a new thermostat because they are motivated (specially after spending several hundred dollars.. It must be worthy), paying a lot more attention in programming it accurately to their needs. That happens with ANY thermostat, including but limited to Nest.