I first heard about this a couple years ago and the whole concept sounded a bit dubious. Apparently the guy responsible for the Ipod design at Apple started a company to make a thermostat. It's a beautiful design, a retro, round thermostat that look really cool. But, even upon first hearing about it, I was a bit skeptical. It has motion sensors in it and it's supposed to come up with a setback schedule based on how it learns your temp settings and occupancy patterns. It was a thermostat for those too lazy to spend 15 mins figuring out how to program one of the typical digital ones. For me, it made little sense. But, I could see it being used in say vacation rental properties.
Recently, I got a little more cuious and started to check it out. Anyone that's interested in a good laugh, should see the reviews at Amazon. What a cluster f**. From reading the reviews, apparently some of the major problems are:
It lacks a hold button. So, this thing that makes up schedules on it's own, can set the temp to whatever it pleases and you can't just set a temp and select to hold it. Could anyone be so dumb as to not include that? And they've been told for years now that customers say that's a big problem. You come home from work sick, set it to 72 and then it just proceeds to do whatever it wants and you don't even know what it plans to do. So, 30 mins later, it could be back to 60F and without checking it constantly, you wouldn't even know.
In the interests of widespread compatibility, they pretend it can work with systems that don't have a wire for power. So, they try to steal power to charge the battery from the wires coming from the furnace. That was probably OK when everyone had an old furnace with a Xformer and relay. But now furnaces have circuit boards that use little current. Net result, the battery doesn;t get charged. And in an attempt to charge it, the Nest apparently fires up the HVAC even when it's not needed. but even that doesn't appear to work.
To try to fit 10lbs of stuff into a 2 lb little round thermostat, apparently they put FET transistors into the base, instead of using relays like most thermostats. The FETS are apparently failing all over the place and when they fail, they fail ON. So, you have many people reporting that the Nest has either the heat or the AC on constantly. Some have BOTH on at the same time! There are reports of people coming home when it's 20F outside and finding their AC running. And this from a widget that was gonna save you money.
Then there is the self-heating problem. It has wifi built in, which I'd want in a new thermostat. But, cramming that 10 lbs of stuff into a 2 lb bag apparently has resulted in the unit self-heating. So people are saying that the house is 75 but the thermostat thinks it's 80, so it's running the AC.
Then there is the issue that since it's wifi connected, Nest can download new software to it at any time and you have no option to decline. Apparently they just did such a download, and it drained people's batteries so the thing no longer worked. Would you not have an option to be able to choose when you do an upgrade on a mission critical device?
It;s really an unbelievable example of making something cute without regard for reliability. IMO, it's a bunch of hippies with no HVAC experience trying to trick people into something that's cool for $250.
And to top it off, Google just bought this pile of crap for $2bil. Unbelievable.