Originally published at: https://tidbits.com/2018/04/20/a-prairie-homekit-companion-the-ecobee-4-thermostat/
Josh Centers is back to smartening up his home with a smart thermostat, the Ecobee 4. But it may be more than he bargained for and way more than he needed.
To quote from one of many sources, " The common wire in an industrial electrical circuit is the neutral wire or ground wire." Josh’s explanation, taken from his linked Q & A answer by ecobee CEO, Stuart Lombard, says roughly the opposite, that the common wire is the power lead. I found another smart thermostat link, which says something similar, in an even more confusing way. I find it bothersome that ecobee and others in the smart thermostat market seem to have invented their own electrical terminology, which runs counter to the standard of the last hundred plus years. For anyone installing a smart thermostat, it may be important to understand this “double” standard.
Thermostats have their own wiring and specific colors. Red for 24V AC power, white for the heat, black for the 24V AC common, yellow for cool, and I forget what orange is as I’ve never had it. the Common is not a ground wire, and it provides continuous 24V AC to the thermostat (for things like powering the LED and such).
I don’t think the C wire in the separate 24V thermostat circuit really has anything to do with the neutral/ground of the 240/120 industrial/house wiring you are referring to.
I agree, Tom, that this isn’t industrial or house wiring. On the other hand, when I last did electronics a couple of decades ago, where 5 volts was often “high voltage”, and 1.2 volts was normal, we still used the term “common” for the ground or neutral, and not for the power.
Re the schedule feature, the complaint in the article is pretty hollow. The point of a programmable thermostat is to save money by eliminating heating and cooling costs when you are not there. If you are always there and want the temperature to remain constant, the thermo has no opportunity to help you. For many other people, me included, that scheduling means money in the bank!
A key benefit of Ecobee that wan’t mentioned in the article is the information available on the web site. Being able to see exactly how your system reacted (by day, week, month and year) to your settings and the outside temperature gives a deep understanding of how your choices influence your costs. Changing your nighttime set point a couple of degrees cooler in the winter, for example, can noticeably reduce the amount of time your system runs. The data provided can really motivate a positive change. Nest and Lyric don’t give you anything like that, as I understand it.
Craig
“I suspect that letting the house get that cold may have cost more money.” You would be wrong. If you kept it warm it would have pumped out heat more rapidly since the thermal differential is larger when the house is warmer.
Perform this thought experiment: Do you think it would have saved energy to let the house cool if you were gone for a year? A month? A week? A day? An hour? The answer to all of those has to be yes. At some point it may not be yes because of the energy needed to heat the furnace up, but that is likely to be in the minutes category and the house wouldn’t cool fast enough to trigger in minutes.
Actually, there’s more than just simple thermodynamics at work here. Some heat pumps will turn on an additional resistive heating element when the heat differential is high to heat the space more quickly. That resistive heating can cost twice as much per joule of delivered heat. So there are situations where maintaining a temperature with a heat pump costs less than allowing a space to cool then playing catch-up with resistive heat.
That’s one place where smart thermostats can make a difference, by being a bit better at predicting those situations (or starting a heating cycle early so as to avoid the need for resistive heat).
Info: https://nest.com/support/article/What-is-Heat-Pump-Balance
Gee, Josh, tell us what you really think.
My experience with the Ecobee thermostats is the exact opposite of yours. I was offered an unbeatable price by my local utility and decided to give the Ecobee 3 a try. It was easy to install and set up. The most difficult part of the project was getting it paired with HomeKit although that has become easier with a subsequent Ecobee software (firmware?) update.
When I have had a question, I’ve found the company’s Tech Support to be excellent. The folks to whom I’ve spoken are friendly and very knowledgeable. The first Ecobee worked so well I eventually replaced my other two thermostats with an Ecobee 4 and another 3. You mentioned the Honeywell Lyric 5 which was one of the thermostats I replaced with an Ecobee. The Lyric 5 cannot handle zones although the Lyric 6 can and so can the Ecobees.
My favorite Ecobee feature is the remote capability. I use a single one with two of my Ecobees and two remotes with the remaining one. We have a downstairs guest room that guests always keep separated from the thermostat sensing part of the downstairs by closing the bedroom door. This causes their room to become considerably colder or warmer than the rest of the downstairs depending on the season. Placing a remote in the guest room has completely eliminated that issue.
Another feature I enjoy is the ability to set a vacation schedule in advance and only have to do it one time for all three Ecobees since they are all on the same WiFi network. One can even set multiple vacation schedules in advance. This capability was added relatively recently and is very convenient for somebody who travels frequently.
All-in-all, I find the Ecobees to be the best “smart” thermostats I’ve owned so far, and I’ve tried quite a few over the last decade or so.
How does the Ecobee 3 support zones. I have a 2 zone house (heat pump and
gas furnace/AC) and never thought that a themostat might provide special
support. I didn’t see information on the Ecobee site. What is there magic
sauce?
Yes, thank you Ron, you beat me to it. I go into this in great detail in page 140 of Take Control of Apple Home Automation where I discuss the Coefficient of Performance (COP) for heat pumps. The COP of an auxiliary heating coil is 1.00, meaning it’s 100 percent efficient, while my heat pump has a COP of 3-4, making it 300-400% efficient. So the auxiliary heat literally costs about 3-4 times as much to run!
I have the Ecobee set to automatically control my auxiliary heat, but it seems to usually kick in when the temperature is 2 degrees below where I’ve set it. So long story short, when it’s at 64 and I want it to be 72, it’s going to cost me a bit extra to bridge that gap.
Yes, that is what I’m often paid to do! 
I’m glad you’ve had a good experience with it. I don’t think it’s a bad product, I just wish it were a bit more streamlined and that I could turn some features off entirely.
I’ll also add that it’s tricky to review things like smart thermostats, because the experience can be wildly different from house to house. For instance, I’m having to explain to our Japanese translators how Americans heat our homes, because the Japanese use very different methods to heat their homes. They think it’s insane that I turn the heat on when the house is 64 degrees inside! (And honestly, they’re probably not wrong, but that’s another article and another thread.)
I wired the Lyric 5 up exactly as the HVAC company wired up the thermostat they installed, but it didn’t function correctly. I called Honeywell, and they told me I’d have to get the Lyric 6 if I wanted to use it with my two zones. So, I tried the Ecobee 3 instead, and it worked fine using the same wiring scheme.
That being said, I’m not sure you and I are talking about the same thing when we use the term “zones”. I have the same system as you do (heat pump and backup gas furnace), but my HVAC company refers to that system as “dual-fuel”. The zones to which I’m referring permit the same HVAC system to send heating/cooling to only one part of my house or to only a different part or to both together by means of a controllable damper valve in the ductwork. In any case, the Ecobees work fine.
Thank you for the response. There are two ways of creating multiple zones.
One is to have a single HVAC system but use dampers to heat/cool different
parts of a house differently. The other is to have completely separate
systems (they can use the same fuel or different fuel). It makes sense that
a thermostat with remote sensors would work with the former but not the
latter.
That is my problem with these smart thermostats. I would need to buy 2 of
them. It would take a long time to save enough on power to pay them off. I
just try to keep my house as warm as I can stand in the summer and as cold
as I can stand in the winter.