Top critical review
Has a tremendous amount of potential, but can't recommend in current state
December 17, 2013
I'm an HVAC contractor who's installed and troubleshooted this product in customer's homes for the past couple years and experienced the good, the bad, and the ugly. Let's start with the good.
-It looks great. Personally I don't really care what my thermostat looks like but I know that is very important to many people and the Nest is unmatched in this area.
-When it works, it is hands down the easiest thermostat to install. The ability to sense wires and automatically configure the thermostat is a cool feature you don't see too often. They have a nifty wizard on their website that where you check the wires you have and it figures out what type of system you have and whether or not it will be compatible. Not that I really care, since this is what I do for a living, but for DIYers who have never done something like this before, it's nice.
-In theory, it can control quite a wide range of HVAC systems, including 4 stages of heating, 2 stages of cooling, dual fuel systems, and humidification/dehumidification.
-The customer service reps do genuinely seem to want to help, and there have been cases of them giving refunds even outside of the return period, or paying for visits by HVAC contractors to troubleshoot issues or repair damage caused by the thermostat.
-The auto away and auto learning seem to work as advertised for the most part and IF, a big IF, you didn't program your previous thermostat, they will save you energy. However your money would be put to much better use by spending 10 minutes reading the manual of your traditional thermostat and programming it (even if its unintuitive, it's not something you have to do often). Then, take that $250 and put it towards something that will REALLY save energy, such as tightening up your house.
-It has energy reporting which the Honeywell wifi thermostats lack (although the Honeywells are better thermostats in every other regard)
-Reliability has been less than satisfactory. Instead of using good old reliable relays like most thermostats Nest decided to use what they call FETs (Field Effect Transistors) to control the equipment. They probably did this so they could give the thermostat its small form factor. Unfortunately, they aren't so reliable and tend to fail in the on position. The Y terminal (compressor) seems to fail pretty frequently causing A/C to run in the winter, sometimes at the same time as the heat. Some people do not have this issue, but for those that do, it seems to happen again and again no matter how many new baseplates Nest sends out. IMO it doesn't matter how many people don't have issues, the technology is plain unreliable and they need to stop using it. Besides the FET issue, software updates are pushed to the thermostat and the user has no choice on whether or not to accept them. Sometimes, they have bugs. The most recent one, 4.0, which the only purpose of was to add support for the Nest Protect, caused issues with some thermostats unable to power themselves. Some Nest owners found their thermostats unable to connect to wifi. Others found their pipes frozen as the Nest failed to turn on their equipment. Again, not everyone had an issue. But a thermostat is not an iPod. A buggy update is going to cause a much bigger problem than being without your music if you are part of the group that does have problems. They need to stop forcing updates on people (have a way to apply them at will) and test them extensively on their own systems before release.
-It's a power stealing thermostat. One big issue when you upgrade to any wifi thermostat is how to power it. To understand this issue, I will give a brief history of thermostats. Back in the old days, we had simple mercury thermostats. No need to power them at all! But then along came digital programmable thermostats. They needed power for their displays, memory, and possibly a backlight. The most common HVAC system in US consists of a basic single stage gas furnace, matched with a single speed central air conditioner. To control this setup, you need four wires in your wall going to your thermostat. This worked fine for old mercury thermostats. To actually enable the thermostat to power itself, though, you need a 5th "common" wire. But, most people only had 4 wires going to their thermostat location. Programmable thermostat manufacturers came up with two solutions to this. The most common solution was to make the thermostats battery powered. These were simple enough to install and worked fine, the only con was that you had to replace the batteries periodically. Another solution was called a "power stealing" thermostat. This thermostat robbed enough current from the HVAC control wires to power itself, but NOT enough to trigger the HVAC system. On older HVAC systems that just ran off relays, this worked fine. Fast-forward to the age of wifi thermostats. How to power these things? AA Batteries wouldn't work, because the wifi drew too much power. What MOST wifi thermostat manufacturers decided to do was FORCE customers to run a common wire to power the thermostat. Nest was not satisfied with this as they wanted to make their thermostat easy to DIY install, so they decided to implement power stealing. Nowadays, though, most HVAC systems run off control boards, which are often sensitive to attempts by a thermostat to rob power for itself and may not let it at all. So sadly, the Nest actually works better with old standing pilot furnaces than newer efficient ones, even though it is a thermostat that promotes efficiency. Huh? Luckily, Nest gives you the option to connect a common wire if you have one, so you don't need to rely on the power stealing. Unfortunately, this issue has just led to too many problems and too much confusion by consumers who thought that Nest would work with their system and then found they needed a common wire. As you can see, not everyone will experience issues, but enough will that it is not OK to assume it will just work, and also it is possible for problems to occur even if it has been working for a long time due to changes in weather and battery capacity.
-"Heat Pump Balance" DOES NOT work as advertised and not only will it not save energy, it will use MORE by running backup aux heat way too much. You can turn that off and set your own lockout temperature for aux heat, but the minimum is only 35 degrees. Most modern heat pump systems can hold their own own down into the 20s. THIS IS A REALLY BAD BUG, IT AFFECTS ALL HEAT PUMP USERS. BE WARNED!
-It doesn't run multistage systems properly. If the Nest detects 1st stage is not keeping up, it will kick into 2nd stage. Fine, most thermostats do this. But then, instead of dropping back into 1st stage, it will stay in 2nd until it shuts off, decreasing comfort and efficiency. Finally, when recovering from a setback, it will ONLY use 1st stage, which takes way too long and makes it difficult to recover in time.
-Technical support isn't so great. Lately there have been ridiculously long hold times, and they don't seem to know what they're talking about. They are polite and professional, though, and I don't blame this problem on the agents, I blame it on the fact they aren't trained properly, which has to do with the next con...
-The overall attitude of the company. They do not communicate with their customers adequately to alert them of updates or problems. There is a community forum on their website that is quite helpful, and I highly recommend you visit it before purchasing. There used to be Nest moderators there, but they have all but abandoned it. There are many Nest users there though who put a lot of time into helping people solve problems and giving advice on how to best use Nest products. There are many complaints there, but they aren't "bashing" the products. Instead they give constructive criticism to Nest on where to improve, and ask for basic updates on what Nest is doing and whether they will fix these numerous issues. Unfortunately, instead of responding to the community members, they decided to make it un-indexable by search engines so prospective customers would NOT see this information. You can see for yourself. Go to [...] and view the source code of the page. You'll see <META NAME="ROBOTS" CONTENT="NOINDEX, NOFOLLOW" >. You can click "recent discussions" to see what people have been posting and feel free to create an account and ask any questions you may have.
-No adjustable temp swing or cycles per hour (other than selecting between radiant and forced air heat)
-Can't adjust % RH setpoint for humidifier automatically based on outdoor temperature
-Their implementation of emergency heat for heat pumps doesn't work well with the majority of systems installed (see the comments thread for more detail).
-The energy reporting is kind of lame. It pales in comparison to Ecobee. Not enough cold, hard, data and too many meaningless statistic like "leaves".
-No hold mode. Really guys, $20 programmable thermostats have this.
Conclusion: Would I recommend this product? Not currently I wouldn't. If you have a heat pump or multistage system, I absolutely would not recommend it. If you have your heart set on this thermostat and have a basic single stage system, be prepared that it may not work without a common wire, and be prepared for the possible reliability issues. Watch it closely after you install and be ready to return it within the 30 day period if necessary. And really, not even considering the reliability issues, is it worth it? I'm not convinced.
UPDATE 1/13/14: Nest has released a new version of their software, version 4.0.1, which claims to have all the new features of 4.0 but the performance of 3.5.3. The jury's still out on whether it does what they say it will: some people are reporting different issues they didn't have before, others say it fixed their issues. The good news, though, is that there is now a moderator on the Nest community, Brian, who is answering people's questions and helping them get the updates they need. While they still have a long way to go, it is good to see them moving in the right direction. Also, for those who don't know: Google owns Nest now. Make of that what you will, I won't comment on the privacy since everyone has a different opinion on that, but I am optimistic that the Google acquisition will accelerate the development of the product.