Thermostat? Daunting

There are plenty of thermostat threads here. But I’ve searched them, and am not quite finding the info I need.

First off, I don’t need a ‘learning’ thermostat. Not only are they pricey, but I have pets with special needs for whom too severe a temp drop might be injurious to their health.

That out of the way, here are my thermostat requirements:
A) Single thermostat that controls both AC and heat on one central system.
B) battery powered; the Rheem system it will be controlling does not have a C wire to power it.
C) should be able to be set to heat or AC mode without a hard switch.
D) must be controllable via Alexa.
E) would be nice if controllable via SmartThings, but not absolutely required.

Obviously the running solution to date is Z-wave, controlled directly via SmartThings, with Alexa controlling it also (indirectly) via SmartThings. I’m very open to that, IF I’d be able to say “Alexa, turn the heat up a degree” tonight and it works, and then tomorrow if the temperature outside rises significantly say “Alexa, turn on the air conditioning” and that works.

So then… who has had great success with such a configuration? Which thermostat are you using?
And if there isn’t really a solid solution yet, I’m open to knowing that too. I’m in no hurry here. It’s just that someone in the family wants to give me a gift, and a thermostat (IF it works well) might be the ticket.

I’m not pushing Ecobee here, since you seem predisposed to a Z-Wave solution…but just as an FYI, the lack of a C wire does not necessarily mean you need battery power (which is something that I’d look to avoid if at all possible). The Ecobee3 series t-stats come with a “power extender kit” that allows you to power the t-stat without a C wire (assuming you have the other requisite wiring available).


Plus Costco has them on sale with 4 remote sensors for $200! Deal!!!


Yeah, I just now saw that. So…then maybe I am pushing it. :wink:


I’m on chat with ecobee support - they say I need a Common terminal on the Rheem to connect

That is the ‘C’ wire, is it not??

Yes, that is for C wire. They also included the kit for the system that does not have the C-wire.

Thanks, I thought as much. The ecobee tech guy was clearly unclear on how his power kit works lol

The C wire is the -24VAC and is just used to power the thermostat so you do not have to use batteries. Ecobee 3 and 4s come with a power module you install in your furnace that gives you that 5 wire function in only 4 wires.

In 5 wire;
Red +24V
White Heat
Yellow A/C
Green Fan
Blue Common (-24V)

In 4 wires, you connect that PEK module into your furnace. The furnace has that C terminal. You just take all 4 wires out of your furnace control board and connect them into the PEK module. The PEK module has 5 wires so they get connected to the control board in the terminals above.

At the thermostat end, the “Green” wire becomes the common wire.

4 wire after PEK module
Red: +24VAC
White: Still heat
Green: Common now.
Yellow: Special PEK terminal.

My guess is that ecobee does something with that wire to send it one way to denote fan and another to denote AC and fan and the PEK energizes either the yellow and green on the 5 wire side or just the green. Fan always comes on when AC comes on. That is what keeps your evaporator coils from freezing up like an old freezer. The constant air going through them to trade send its heat energy to the coils to be dissipated by the condenser outside.

I have a 4 and love it. And the $200 deal at Costco is great but you might check with your local utility for added rebates on top of that. I know AmerenUE in St. Louis is giving you a $100 rebate. So, in St. Louis, that would be just $100 if you factor in the rebate.

Thanks. You prompted me to do a bit of research. I already had photos of the thermostat and the schematic for the blower from a previous thermostat-replacement conceptualization.

So in the blower, the wires are as follows according to the schematic:

White: HEAT
Green: FAN
Yellow: COOL

In the existing thermostat, the White Green and Yellow wires are in the correct terminals - with the Red wire in RC, and a jumper between RC and RH.

On the schematic, the above Red wire is emanating from a terminal on the Heat Cool Relay labeled ‘R’.

There is another terminal, labeled ‘C’, which has low-voltage wires going to other components.
Presumably, this is the Blue Common terminal in question.

Interestingly, I have easy access to the wall where the existing thermostat is mounted. So I could easily do a new low voltage run with 5 wires, and bypass any need for the PEK module.

Btw, costco’s Website says the Ecobee3 are out of stock and can no longer be added to your cart.

Amazon still has them, both the regular and Lite versions.

ETA: Never mind. I forgot about CostCo having them on sale.

dont buy ecobee
waste for what you want

buy a basic thermostat
Radio Thermostat CT50 7-Day Programmable Thermostat (WiFi Enabled), iOS & Android App Controls

there is a smart app developed by a developer in the forum

i know the app says it works with 3m-50, but its the WiFI module that it works with that the thermostat above has. you can buy used for $60

dont have a c-wire? no problem
you will need this
Venstar ACC0410 Add-A-Wire Accessory for All 24 VAC Thermostats (4 to 5 Wires), White

you cant run a zwave or wifi thermostat needed for a smart home without a c wire. the batteries would depleted so fast

heres a how to video for the ‘add a wire’ device

there are other how to videos without buying a device but i dont recommend bc you would lose functionality typically of the thermostat fan.
the venstar device gives you all functionality

great news is since the thermostats will be compatible with smartthings then it will be with alexa too.

hopefully you understand this solves every problem🙂

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Actually, while you’re fundamentally correct there would be one big plus to ecobee: WAF.

So much of what I’ve done with my smarthome has been me dabbling, conducting a science experiment.

But where the thermostat is concerned, my wife will be interacting with it far more than I. So a plug-n-play thing that “just works” with both ST and Alexa without me having to concern myself about github etc might be valid. And the ability to add sensors in the future just might come in handy.


is it worth $100 more? the smart app is barely updated. you dont have to create a github account. just cooy paste the code. its been updated once in the last year and the update was just appearance but i only use for the connection. ive had this thermostat for 6 years and ST for 3. I dont have to worry about ST and the ecobee cloud not working together. just my own network. but whatever you do, definitely use the add a wire device. definitely not worth it to run a wire. man that would be a headache

Apparently, you’re not married. LOL


oh i am 7 years :stuck_out_tongue_winking_eye:

my wife loves that she never touches the thermostat and ive only had to update the app once

plus the thermostat i have in mind for you has an app too
Radio Thermostat

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The Ecobee3 Lite can be had for $169 w/free Prime shipping from Amazon. The solution you describe would cost $118 just for the components, not to mention the time and effort of making it all work. And then you won’t even have any support for the system, nor the amount of functionality. The $51 difference is money well spent when it comes to a thermostat.

I installed a GoControl thermostat a couple of weeks ago. It’s working perfectly. I don’t have a c-wire either and I was concerned about battery life but I asked around and people say it’s fine. I use WebCoRE and wrote routines that manage the temperature based on presence, time of day, doors being left open, etc. I’m also writing on/off cycles to a spreadsheet. And I get a text message when someone adjusts the temperature (it seems there are “thermostat gremlins” in my house :wink:). It’s a pretty simple device but I can do anything I want with it using WebCoRE. Installation was a snap and it’s cheap. And you can use Alexa to control it.

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I use the other room sensors for other things, like automatically turning on ceiling fans if they get too hot and the motion detectors, for now. I realize that there is a delay on these motion detectors. That and the added Alexa microphone and speaker are worth the $100 for me (which Ameren refunded with a rebate, so it cost me nothing, and they were running a sale on the web site that gave you two extra room sensors for free).

I have been pestering Ecobee about the ESP function (Echo Spatial Perception) and adding it in as far as the all-music group and they say they are actively working on it.

Plus, I am getting reports about how my house is fairing as far as energy consumption. I have a relatively new furnace installed in 2013 and when I was doing my research, I found it was capable of two stage operation with the additional thermostat wire and moving one jumper on the control board. (I was laid up with an injury and work was not letting me work so what else was I supposed to do?) Now that the furnace is back on after summer, it is going to be interesting to see how more efficient it is by running mostly one stage one instead of always on stage two, so its longevity should increase, plus I keep it maintained…just changed the filter that I am supposed to only have to change once a year, today, because I change it twice a year.

The Ecobee has a build-in humidistat in it, too and felt that with it being upstairs instead of the humidistat on the cold-air return would be more reactive to things, like taking showers and making dinner if I was boiling water to reduce the humidity in the house by not running the humidifier when those activities are taking place. On my system, I have to use two wires for the humidity function because there is a +24V humidifier terminal on the furnace’s motherboard and it needs the -24V return to the common wire. That terminal only provides power when the system is on in heat mode.

So, when I installed it, I ran a 7-wire and a 5-wire thermostat wire.between furnace and thermostat so I have all my wires in the wall now, in case there are any future upgrades to the system. I used the old 4-wire as a pull-string in the wall to get them up. So it was not that bad. Luckily, the old one was not stapled to the wall in the stud cavity.

Ultimately, it is your decision but these are a few of the things that justified the extra cost of this thermostat over the others and I did a lot of research on picking one out. If it is not good information for you, maybe it would spark interest in others reading this thread.

There is something nice when being in bed and waking up too hot or too cold to tell Ecobee when you are half-asleep to raise the thermostat or lower it.

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The Ecobee ended up coming my way :slight_smile: Without the external sensors, but that’s fine by me. I’ll apply for the $75 rebate with my local utility…

So i’ll Install it next weekend, using the supplied kit with my existing wiring.