FAIR WARNING: THIS REVIEW IS A BEAST. Therefore, for readability’s sake, I’m dividing it up into sections.INTRODUCTION:Today, 4/13/2016, marks my third major revision to my original 10/20/15 review. That review gave the ecobee3 4/5 stars. This revision awards it the 5th star that it deserves.At the time of this third revision, there are 3 separate versions of the ecobee3 available on Amazon: this product (the 2nd Generation ecobee3), the ecobee3 Smarter Bundle (which is the same product, except it includes 2 additional remote sensors), and the original 1st Generation ecobee3 (which is still on Amazon but is no longer for sale by Ecobee).I bought the Smarter Bundle to replace my 2nd Generation Nest Thermostat, which I had in my house for over a year. Keep in mind that at the time of this third revision, Nest is selling the third generation of their flagship product. This review compares the ecobee3 to the 2nd generation Nest; however, my understanding is that the Nest 3’s only improvements over the Nest 2 are a larger screen and a more sensitive occupancy sensor, so all comparisons I draw between the ecobee3 and the Nest 2 are still applicable to the Nest 3.Don’t get me wrong—the Nest was a good product. But, due to many of the shortcomings that I will mention in this review—and the relative superiority of the ecobee3 in those aspects—I am thrilled with my decision to replace the Nest and I do not plan to go back.BACKGROUND:My HVAC is a Heat Pump, which consists of an outdoor AC compressor and an indoor air handler with electric heat strips.I purchased the 2nd Generation Nest Thermostat in May, 2014 to replace the Honeywell Mercury thermostat that my house came with. The Nest was an excellent product in terms of tracking my HVAC usage and granting remote access to my thermostat and all its controls. However, many of the Nest’s original selling features—namely, the Auto Away function—quickly became useless in a real world setting (more on that below). Additionally, my household is primarily an Apple household, so when Apple announced the release of its HomeKit framework and Nest (a Google owned company) intimated that they would not include HomeKit support in their products, I knew my Nest thermostat’s days were numbered. When Ecobee announced that their ecobee3 thermostat would include HomeKit support, I did extensive research into the product, and I took a leap of faith......And it was a damn good idea.INSTALLATION:Several other reviews discuss this aspect of the ecobee3 so I won’t go too far into it here. Suffice it to say, installation is not terribly difficult. You can use Ecobee’s website to check for system compatibility, or, if you are really unsure, Ecobee customer service work with you to verify if your HVAC will work with the ecobee3. In terms of the physical installation, it’s literally as simple as selecting your backplate, doing some mounting, and from there it’s plug-and-play. After that, the software setup is all guided.THE HEADLINE FEATURE - REMOTE SENSORS:The headline feature of this product is its use of remote occupancy sensors. This is the single feature that puts this thermostat head-and-shoulders above all the rest. The remote sensors serve two functions: first, they tell the thermostat when a room is occupied, and second, they tell the thermostat what the temperature is in that room. As Ecobee boasts, their thermostat is for homes “with more than one room.” These sensors are what make this product a rockstar!I live in a multi-story home, and my thermostat wiring is located in my dining room, which is on the main floor of my house. After I installed the ecobee3 thermostat, I experimented with the placement of the remote sensors to determine where they would be best used. Ecobee provides some recommendations, and I’ll include some of my own: don’t place them in a location where they will be exposed to direct sunlight; don’t put them directly over or below vents and registers; try to keep them about 5 feet off the ground; etc. One tip I discovered for myself is that you shouldn't put a sensor on or very close to your TV media stand because that equipment generates a substantial amount of heat, which creates inaccurate temperature readings for that room. Ultimately, I mounted one sensor on my living room wall, one on my roommate's bedroom wall, and one close to the dog cage in my master bedroom. My placement of these sensors was crucial, and here is why.The ecobee3 has a feature called “Follow Me” that uses the remote sensors in conjunction with the thermostat’s internal temperature sensor to heat and cool your house to the temperature set point. In a regular thermostat, such as the Nest, the HVAC will operate until only the room with the thermostat achieves the temperature set point because the thermostat’s internal temperature sensor is the only data point for the thermostat to read; with the ecobee3’s remote sensors, the thermostat monitors the temperatures detected only by the sensors in occupied rooms, and then the thermostat operates the HVAC until the AVERAGE temperature across those rooms equates to the thermostat's set point. You can also program the system to only use certain remote sensors at certain times of day (see “COMFORT SETTINGS” below)—and in my case, this feature was a godsend.One of the problems that my house has is that there is a substantial temperature differential between my main floor and my master bedroom, which has a vaulted ceiling. On hot, sunny days, my bedroom can get up to 8 degrees warmer than my main floor. Because my dog’s cage is located in my master bedroom, this massive temperature differential can be more than problematic; it can be potentially dangerous. Even if I kept my thermostat set to 72 degrees at all times—which negates the purpose of having a “smart" thermostat—my bedroom would still get up to 80 degrees. With my Nest, I programmed the thermostat to raise the AC set point to 76 degrees during the work day to save energy, but the result was that my bedroom would get up to 84 degrees! Not good!This is where the ecobee3 shines!On the hottest of summer days, I had my ecobee3 set to 78 degrees, but I had it programmed to use only the remote sensor in my master bedroom as the sole temperature sensor. As a result, no matter what the temperature was in every other room in my house, I never had to worry about my dog overheating because the ecobee3 would never let my master bedroom get above 78 degrees. Problem solved!Now, as some of you have deduced, the placement of remote sensors in parts of your home that are prone to extreme temperature fluctuations will undoubtedly result in your HVAC cycling more frequently, and therefore increased energy usage. Yes, you are probably correct, but there may have been other factors at play (See “SCHEDULING” below). For example: I compared my September 2015 power bill to my September 2014 power bill and there was an average increase in usage of 1 kWh per day; for August 2015 compared to August 2014, the average increase was 3 kWh per day. Regardless, I consider this change in consumption so nominal that I believe the substantial increase in comfort—and my dog’s safety—offsets the only slight increase in energy cost.THE OTHER FEATURES:INTERFACE - The ecobee3 uses a touchscreen for input, which in my opinion is far more intuitive than the rotary-dial interface pioneered by Nest. Whereas the screen of the 2nd Generation Nest shuts off by default when not in use, the ecobee3 changes to a simplified view that includes the indoor temperature (IMPORTANT NOTE: This is NOT the temperature of the room that the thermostat is located in, but rather the averaged temperature across all the active sensors!) and the outside temperature & current weather conditions—which is a definite plus over the Nest. Additionally, the thermostat’s graphical user interface (GUI) is nearly identical in the iOS app, which is nice for consistency’s sake. The HomeIQ web portal (more on that in the “HOMEIQ” section below) is more similar to the Windows 8 “Metro” GUI, but it is still intuitive and navigable. In terms of aesthetics, I’ll admit that the all black interface of the ecobee3 is somewhat drab in comparison to the bright, vivid colors of the Nest, but I bought this thermostat not for the color of its screen but for the content of its… oh, you know what I mean.COMFORT SETTINGS - By default, the thermostat comes with 3 Comfort Settings: Away, Home, and Sleep. Each of these settings is customizable in terms of pre-programming the temperature set points of both your AC and Heat, and you can also set the specific remote sensors you want the thermostat to use in each Comfort Setting. Additionally, you can create more Comfort Settings, but these 3 sufficed for me. I programmed the ecobee3 to use all the sensors in the “Home” setting, only the 2 bedroom sensors in the “Sleep” setting, and only the master bedroom sensor in the “Away” setting so that my dog can stay comfortable while I’m out. The ecobee3 also includes an “Auto” mode, so the thermostat will use the temperature ranges in each comfort setting to automatically engage your AC or heat depending upon the outdoor temperature and how it affects your indoor temperature.SCHEDULING - Scheduling is fairly standard, but it has some benefits over the Nest. Where the Nest’s scheduling method involves manually setting the temperature set point at different times of day on different days of the week, the ecobee3’s schedule uses your Comfort Settings mentioned above (“Away,” “Home,” and “Sleep”). To me, this method makes more sense than the Nest’s scheduling method. Like the Nest, however, you can program the ecobee3 to use a feature called Smart Recovery, which pre-heats/cools your home to the desired temperature in advance of the next scheduled Comfort Setting. For example, if it is summer time and you have a scheduled Away period from Monday to Friday, 8:30 AM - 5:30 PM, and your Away temperature is 78 degrees but your Home temperature is 72 degrees, then the ecobee3 will begin cooling your home in advance of your arrival so that your home is 72 degrees when you arrive. Keep in mind that Smart Recovery will cause your HVAC to run for an extra time window every day, which means more energy consumption; I disabled this feature with the Nest but enabled it with the ecobee3, which may explain some of the increase in electrical consumption that I noted above in my discussion about the remote sensors.SMART AWAY/HOME - This feature actually makes sense with the ecobee3 and is finally worth using! As many of the Nest’s critics (correctly) note, not all homes have a centrally-located thermostat, meaning Nests with Auto Away enabled that don’t “see” a lot of traffic frequently go into Away mode when people are still inside their homes! My Nest happened to be centrally located, but if I was upstairs in my house for even an hour or two, my Nest’s Auto Away would engage—and trust me, with as rapidly as my house accumulates heat during summer, one notices pretty quickly when the upstairs is becoming uncomfortably warm. This flaw has resulted in a lot of people (including myself) disabling the Nest’s Auto Away, which for me was the main selling point of the Nest because of my inconsistent schedule. In contrast, with the ecobee3, the remote temperature sensors prevent this glitch from happening. As long as the ecobee3 or any of the remote sensors “see” you anywhere in the house, Smart Away will not engage. Additionally, if the ecobee3 detects movement during one of your scheduled “Away” Comfort Settings, the thermostat will override the setting and revert to your “Home” Comfort Setting, which is a pretty nifty touch. Now, granted, the current window for Smart Away to engage is a rather long 2 hours of inactivity, and furthermore, this setting cannot currently be modified by the end user; however, in theory, Ecobee could open up this setting in the future with a simple software modification.HOMEKIT - Arguably, the reason I jumped to this particular thermostat was its HomeKit support. As I mentioned earlier in this review, my household primarily uses Apple products, so I wanted to purchase a thermostat that supports the smart home platform that I am most likely to invest in.In late October, 2015, Ecobee ramped up its HomeKit support (which I noted in my 10/28/15 modification to this review). Ecobee’s HomeKit support does have some perks. I can ask Siri about the temperature of any room with a temperature sensor and she will be able to provide that information without me even having to unlock my phone and open the Ecobee app (SEE PICTURE). The ecobee3 also has support for 5 HomeKit “Scenes": "Good Morning," "Good Night," "I'm Leaving," "I'm Home," and "Resume Schedule." Each of the first 4 scenes corresponds to one of the default Comfort Settings for the thermostat. So, for example, if you say "Good Night" to Siri, then the ecobee3 will change to the Sleep Comfort Setting. This same command, in theory, should shut off all your Philips Hue bulbs and lock your August Smart Lock. The other scenes correspond to their respective Comfort Settings: "I'm Leaving" is Away, "I'm Home" is Home, "Good Morning" is Home, and "Resume Schedule" will revert to whichever Comfort Setting is currently scheduled.IMPORTANT! HomeKit remote access only works if you have a 3rd Generation Apple TV or later AND that Apple TV is logged into the same iCloud account as your iOS device. In my original review, I mentioned that HomeKit remote access didn’t work for me, but it was because my Apple TV wasn’t logged into my iCloud account. My second revision to this review (10/28/2015) noted that as soon as I logged it in, I gained full remote HomeKit access to my ecobee3. Remote HomeKit access continues to work today.GEOFENCING - The final perk of the ecobee3’s HomeKit compatibility is that the HomeKit framework gives the ecobee3 geofencing support. Unless you are using a third party framework (ie. IFTTT), geofencing is exclusive to HomeKit. Geofencing is meant to supplement the occupancy sensors in determining when you are home or away for purposes of engaging the correct comfort setting. With geofencing enabled, when you cross your geofence in either direction, the ecobee3 switches into either the "I'm Leaving" or "I'm Home" scene, meaning the respective Comfort Setting is enabled. This new function is analogous to the headline feature of the much maligned Honeywell Lyric, but my understanding is that Honeywell's geofencing algorithm was shoddy and quite buggy. By implementing geofencing as an additional feature, Ecobee has now bridged the gap between its two biggest competitors—the Nest and the Lyric—by marrying internal occupancy detection to external geofencing and creating a hybrid product that magnifies the merits of each approach while ameliorating their respective shortfalls. This was an absolutely genius move on the part of Ecobee. Furthermore, my above criticism about the occupancy sensors requiring 2 hours of inactivity before Smart Away will engage is remedied by the implementation of this new feature. When used in conjunction with accurate scheduling, the addition of geofencing should save several additional hours of HVAC usage every month, meaning additional savings in electricity consumption!HOWEVER—and this is a big HOWEVER—the current implementation of Geofencing actually OVERRIDES your schedule using the ecobee3's 2 "Quick Changes," which are "Home and hold" and "Away and hold." These "hold" settings ignore your upcoming scheduled comfort settings until you manually disable the hold. This programming poses a possible problem. For example, if you live in a house with multiple people and you are the only person with the Ecobee app on your phone, once you leave the geofence to go to work, the ecobee3 will engage "Away and hold” and it will ignore occupancy detection from all the internal sensors, regardless of whether there are other people in the house; similarly, once you re-enter the geofence at the end of your work day, the ecobee3 will engage "Home and hold," and it will remain in that mode all night instead of engaging the Sleep Comfort Setting. So, be careful with this feature! I am told that Ecobee is well aware of this glitch and is actively working to fix it, but until then, I do not use geofencing and therefore I can’t endorse this feature.TEMPERATURE TOLERANCES AND HVAC CYCLING - This is a weird one. I’m not a professional HVAC technician, so take this one with a grain of salt. My understanding of these thermostats is that the Nest has a greater temperature threshold (1 degree) than the ecobee3 (.5 degrees, but is customizable). As a result, the Nest cycles your system less frequently but for longer periods of time, whereas the ecobee3 cycles more frequently but for shorter bursts. There are multiple schools of thought here as to which approach is better (ie. Energy efficiency, wear and tear on the system, etc.), and I will decline to offer my uneducated opinion. However, I do like that I can customize this setting on the ecobee3.HEAT PUMP BALANCE - This was a major change for me. Before I go into a comparison of the ecobee3 to the Nest, I’ll just do a quick primer for those who do not understand the mechanism of a heat pump.Essentially, a heat pump reverses the action of air conditioning; air conditioning transfers heat from inside of your house to outside, which makes the inside cooler, whereas when the thermostat engages the heat pump, a reversing valve reverses the flow of your refrigerant and transfers the heat from outside of your home to the inside. This method of heating is extremely efficient, but it’s slow and methodical. However, when the temperature outside falls below a certain “balance point,” the heat pump can no longer effectively harness ambient heat from the outside air, and then a secondary heating system—the auxiliary heat—must engage to heat your house. The auxiliary heat system is essentially just an electric furnace that uses electric heating strips to create radiant heat, and then the main HVAC fan returns air from your home into the air handler, circulates that air around the heat strips, and then circulates it through your home. This method of heating is effective and quick but relatively inefficient—and it is also very expensive.Now, with the science out of the way, let’s return to the discussion of the thermostats. During set up, by default, the Nest gives you 3 options on a continuum for Heat Pump Balance: “Max Savings,” “Balanced,” and “Max Comfort.” With Max Savings, the thermostat will run the heat pump for longer periods of time in order to avoid having to engage the auxiliary system; in contrast, with Max Comfort, the thermostat will resort to auxiliary more quickly and frequently to warm up the house in less time. The theory underlying this algorithm is that X hours of the heat pump running equates to Y minutes of the auxiliary heat running, so if you emphasize savings over comfort, the system will prioritize the use of the heat pump for longer periods of time over running auxiliary for short periods of time in order to save power, and the thermostat will only resort to the auxiliary heat as a last resort. Problem? In the Nest’s effort to keep setup simple, it uses its own preprogrammed auxiliary lockout temps when you select one of these settings. The result was that in the 2014-2015 winter, because I selected Max Savings, my heat pump ran for literally HUNDREDS OF HOURS when the climate was too cold for my heat pump to function at all! In contrast, during set up, the ecobee3 immediately presents you with the option to manually set both your heat pump compressor lockout and your auxiliary lockout temperatures.At the time of this third revision to my original review, the 2015-2016 winter has (mostly) ended and I can surmise in good faith that the ecobee3 made a positive difference in my bills. The major reason for the improvement is that the ecobee3 helped me to determine my heat pump’s balance point. The online HomeIQ data (more on that below) demonstrated with crystal clarity (SEE PICTURE) that my indoor temperature would steadily decline even with the heat pump running if the outdoor temperature was 25 degrees or below. Because these metrics were available to me, I set 25 degrees as my compressor lockout setting, which meant that my heat pump wasn’t running needlessly when the ambient temperature was too cold for the heat pump to function, which in turn meant that I saved money on my electric bills this winter. In contrast, the Nest doesn't give you enough data to make this determination, so the ecobee3 wins spectacularly in yet another aspect!OTHER FEATURES - There are a lot of other features as well—too many to go into here. It’s clear that Ecobee intended to create a granular product that the end user could micromanage down to the minutiae. A couple of the additional features include fan scheduling, Alerts and Reminders (ie. maintenance reminder, filter change reminder, UV lamp reminder, low/high temperature alerts, low/high humidity alerts, auxiliary heat runtime alert, and auxiliary outdoor temperature alert), Vacation scheduling, heat set point range, cool set point range, etc.THE WEBPORTAL AND HOMEIQ - Ecobee’s Website has a backend that contains several basic pieces of information about your system, but the most interesting data comes from its “Home IQ” section, which contains sections that provide several fascinating metrics.In terms of the “System Monitor" data, you can see the times at which your HVAC was running, which functions was running (ie. In my case, AC, Heat Pump, Auxiliary, and Fan), how long the function was running for, your heat/cool set point, your indoor temperature (calculated according to the active remote sensors), and the outdoor temperature. Home IQ also tells you how your schedule and Comfort Settings affected your HVAC usage, which remote sensors were used at any given time to activate your HVAC, and how the weather impacted your HVAC usage by comparing a line graph of the average outdoor temperature each day against an overlaid bar graph of how many hours your HVAC ran. All of this data can be downloaded in .CSV format as well, which breaks down your system’s data into 5-minute increments!But that’s just the basic stuff. Ecobee’s usage of your home data goes much further!Every month, Ecobee compiles usage, local weather, and temperature set point data from your thermostat and it uses that data to tell you how many hours of runtime you saved relative to a standard 72-degree benchmark, how much money you saved on your electric bill as a result, and how much money you've saved in total since your registration. Ecobee goes even further by comparing your compiled data against the data collected from the thermostats of all of the customers in your geographic area. Ecobee uses this data to tell you how efficient and inefficient your temperature set points were relative to other customers in your State, and it gives you a Home Energy Efficiency Rating that rates how well your home retains thermal energy relative to other customers in your State.No offense to Nest, but these metrics are way more compelling and practical than a simple total of accumulated “Nest Leaves.”THE FLAWS:Finally, for all the pluses of this product, make no mistake, it is not perfect—hence the original deduction of 1 Star from this review.THERMOSTAT SENSOR OVERHEATING ISSUE - The biggest shortfall of this product is not an insubstantial one. In fact, it can be considered fatal if you aren’t willing to do a workaround. Many reviews note that the internal temperature sensor in the ecobee3 registers as a few degrees warmer than it should. Those reviews are all correct. I tested this error for myself by putting one of the remote sensors right next to the thermostat for several days and monitoring the temperature readings from both the thermostat and that sensor. The readings from the ecobee3’s internal sensor were consistently 1-2 degrees warmer than those of the remote sensor during inactive periods, and 3-4 degrees warmer than those of the remote sensor when the system is running. My understanding is that the reasons for this discrepancy are that some systems send too much voltage to the ecobee3 through the Common wire, which causes the thermostat to run warm. However, I don’t consider myself well-versed enough in the subjects of electrical and mechanical engineering to comfortably discuss those reasons, so I would refer you to Ecobee customer service if you want to know more.Obviously this temperature discrepancy would be extremely problematic if you are running your HVAC using ONLY the thermostat’s internal sensor because your air conditioning would run too long to achieve the temperature set point and your heat wouldn't run for long enough. In terms of an easy remedy to this problem, the workaround is very simple. As I mentioned above, I bought the Smarter Bundle, so my ecobee3 came with 3 remote sensors. To temporarily “fix” the temperature sensor defect, all I did was totally bypass the thermostat’s internal temperature sensor across all the Comfort Settings, and I used the remote sensor in my living room as the substitute sensor for my main floor. It’s an easy fix, but is it really one that I should have had to make considering how much this thermostat costs? Again, I am totally satisfied with my decision to switch from the Nest to the ecobee3, but at least the temperature sensor in the Nest did its job.Nearly 9 months after my purchase of the ecobee3 and a couple calls to Customer Service, I finally took steps to permanently fix the problem. As I mentioned in my December 17th comment to this review, Ecobee customer service recommended installing the Power Extender Kit (PEK) to remedy the overheating issue. For those who do not know, the PEK is a small circuit board that Ecobee includes with the ecobee3 to make the thermostat compatible with those systems that lack a Common wire. I was unsure about doing the necessary rewiring that this installation would entail, but multiple Ecobee representatives that I had spoken to agreed with this course of action because when the PEK is used, the voltage that is sent to the thermostat is metered by the circuits inside the PEK, which fixes the overheating problem.Ecobee customer service spent 1 hour and 52 minutes with me on the phone, patiently and thoroughly running me through the installation procedure. The “surgery” was complicated (because I am colorblind) but it went fine. I did the installation several days ago and I wanted to monitor the system and its readings for a few days before drawing any conclusions. To test whether the sensor discrepancy had been fixed, I did what I had originally done to discover the overheating problem, which is that I moved my Living Room sensor to a position about 1 foot away from the thermostat and I just left it there.As I mentioned above, before the installation of the PEK, the readings from the thermostat’s internal sensor ranged from 2-4 degrees warmer than those of the nearby Living Room sensor when the system was operating.After the installation of the PEK, the difference in readings between the Living Room sensor and the ecobee3’s internal sensor ranged from 0-1 degrees.It worked.The thermostat is now correctly measuring temperature with its internal sensor. Because there is no longer a discrepancy between the thermostat's temperature reading and the actual room temperature, I have finally been able to introduce the ecobee3’s internal sensor into its Comfort Settings for the first time since I bought the thermostat. This extra temperature sensor will provide additional useful metrics going forward, along with a snappier response time for Smart Home and Smart Away.REMOTE SENSORS DISCONNECTING - As other reviews have mentioned, this definitely happens, but it is very rare! Remote sensors disconnect maybe once or twice per month, and it’s never for longer than an hour. I am not bothered by this, as I have 3 remote sensors in my house, but I can definitely see why a person who has only 1 remote sensor might be. But again, for my purposes, I do not see this as a problem because it happens so rarely.LIMITED HOME IQ ACCESS - Currently, Home IQ Data can only be viewed on the web portal. It would be nice at a future date if Ecobee allowed its customers to view this data in the Ecobee app. I shouldn’t have to sit at a computer and log into Ecobee’s website to see my HVAC usage logs. In this particular area, Nest wins because your usage data is accessible from the app and the thermostat itself. Unfortunately, nearly 6 months after my original review, Ecobee still hasn’t added support for this. Hopefully some day soon Ecobee will add Home IQ support to the app.SUMMARY:The ecobee3 is more than a mere thermostat; it is an advanced piece of home automation technology. I believe it is a superior product to the Nest, and I am thoroughly satisfied with my decision to convert.I have said it several times in this review and I will say it once more: I am pleased with my purchase. The internal temperature sensor issue was the final shortcoming that kept the ecobee3 from its 5th Star. Now that it has been fixed, this product has achieved its state of true perfection, regardless of the other shortfalls I mentioned above. Obviously the product can always improve, but in terms of my wants and needs, it is as damn close to perfect as anything I can imagine.So, finally, in summation...This product is the hands down best on the market. But, even more importantly than this product's superior quality is the fact that it is supported by a company that is staffed by employees who stand behind their product.Great work, Ecobee!