Help installing Nest Thermostat E's in new home

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Old 09-26-20, 12:40 PM
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Help installing Nest Thermostat E's in new home

My elderly parents recently moved into a new house. I'm converting their old thermostats to ones they can control with their voice. The most affordable option through their power company was Nest Thermostat Es. I'm having some trouble discerning if these will work with their system.

Here is what's currently in place.

MAIN
Thermostat: Honeywell Vision Pro 8000 (TH8321R1001)
Furnace: Lennox SL280UHV Gas Furnace
A/C: Lennox Elite Series XC14

Wiring at main thermostat:


Wiring at main furnace:



UPSTAIRS
Thermostat: Honeywell Vision Pro 8000 (TH8321R1001)
Furnace: Lennox SL280UHV Gas Furnace
A/C: Lennox 14ACX

Wiring at upstairs thermostat:



Wiring at upstairs furnace:




Some other observations
  • -Both furnaces have variable speed fans which I've read do not work with Nest. However, I'm not sure the current system is even utilizing the variable speed.
  • -Under the setting "FAN CONTROL IN HEAT" both thermostats have "equip controls fan" instead of "tstat controls fan."
  • -Both current thermostats have "DEHUM EQUIPMENT" enabled in settings. The downstairs has "A/C with high fan" while the upstairs has "A/C with low fan".
  • -The upstairs system has a U1 wire which seems to be wired up for the dehumidifier setting of "A/C with low fan."

Some questions
  1. 1. Can I use the Nest thermostats with a variable fan system? I'm assuming I just lose the variable fan functionality (which may not even be in use already)? If not, do I need to look into other options, like the EcoBee?
  2. 2. The main level seems to be a pretty basic configuration. The lack of a C wire seems to create problems with smart thermostats. The nest supposedly works, but it will sap some volts from R (I think). I do have two terminated cables on both ends though (yellow and brown). Can I repurpose one of these as a C wire?
  3. 3. Given the minimal wiring of the main thermostat is there anything special about the "A/C with high fan" dehumidification. Is that setting actually controlling specialized hardware or is it just turning on the A/C when the thermostat senses humidity above a certain level? If it's the latter, then I think the Nest can do the same thing, right?
  4. 4. The upstairs unit seems to have specialized hardware for dehumidification (via U1). Is it possible to adapt this to work with the Nest?
  5. 5. The main isn't wired with U1, but it's the same furnace. Should this be wired up or do I really only need one unit dehumidifying?

I know this is a lot. I tried to include as much information as possible. Please let me know if I forgot anything! Any help here would be appreciated!
 
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Old 09-26-20, 02:08 PM
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Two good thermostats..... a shame to remove them.
The nest e is the basic no frills thermostat. It will not control anything variable.

Strange.... two spare wires and they weren't used ?? The stat should have had the C connected and been wired for two stage heating. It can be done in the future.

Second floor was wired for two stage operation.
I don't know why both floors weren't connected similarly.

The nest e will support two stage heating but no extra fan switching like the second floor is using.
 
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Old 09-26-20, 03:03 PM
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I assumed the old tstats were probably better in terms of controlling in the hardware, but the truth of the matter is that my parents are elderly and they're looking for ease of use. For instance, they will rarely go upstairs. It would be great if they can control it remotely. Also, I think they'll appreciate the use of voice commands through their Nest Hub. I'm not opposed to another smart thermostat, but these were the ones offered at discount through their EMC. The EMC also offers a discount on the EcoBee, but it's more expensive. Is there something else you'd recommend? Can I get by using the Nest E safely? Also, on the main unit, is it as easy as just hooking up one unused wire to the C on the furnace and C on the thermostat while keeping all the other wires the same? Lastly, I have an HVAC tech coming out on Monday for bi-yearly maintenance. I can ask them about why the two units are wired differently.8.4.3
 
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Old 09-26-20, 05:08 PM
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Just be warned, the Nest thermostat has proven to be extremely unreliable. Lots of odd issues and problems. Some have shorted and actually caused equipment damage.
So your parents may require increased service for Nest troubleshooting.
 
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Old 09-28-20, 07:53 AM
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Despite everyone else on this board, I've had continued success with my Nest thermostats for the last 8 years. Of course this might be due to the use of a "C" wire for all of them.

However - for my main floor heat pump system I do have a Honeywell 8000. This is what the HVAC contractor installed; I left it in place because it uses an actual outdoor sensor to work with the heat pump. I know the Nest can provide similar functionality, but it does it via Internet sourced weather data and not an actual sensor.

I'm not sure how Google Home or Nest type systems handle RedLink items, but I do know I have Alexa fully integrated. "Alexa, set the living room to 72 degrees" will result in the thermostat adjusting to match.

To get my Honeywell thermostat on the Internet I used a gateway plugged into my router. The model I used was THM6000R1002 (https://us.amazon.com/Honeywell-THM6.../dp/B006BD1K4A). I see there is a newer model THM6000R7001 (https://www.amazon.com/Honeywell-Red.../dp/B0783HK9ZZ).

Rather than updating to Nest thermostats, I would just go down the Internet gateway path first. Much easier and likely cheaper.
 
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Old 09-28-20, 03:38 PM
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Rather than updating to Nest thermostats, I would just go down the Internet gateway path first. Much easier and likely cheaper.
I actually just ordered this part this morning before you posted this. I didn't realize I could get the current 8000 tstats online using RedLink. I went ahead and ordered that part for $65. It should be the cheapest and easiest solution. This way, I'll also have the use of all stages of heating and the low fan for dehumidification. My parents won't know the difference. I'm betting it all looks the same through the Google Home app anyway once it's connected with Honeywell.

Strange.... two spare wires and they weren't used ?? The stat should have had the C connected and been wired for two-stage heating. It can be done in the future.
I had an HVAC tech come out from the company that had installed both units in the house. They agreed that the main unit had been wired incorrectly. They used the two extra wires and reconfigured the unit to use a common wire and added the second heating stage. The only thing they couldn't wire was the "low fan for dehumidification" since there weren't enough wires. They said I could get a wireless transmitter to effectively add this ability. He described it as a transmitter on both ends (thermostat and furnace) which effectively adds an extra wire. It's actually a pretty easy run into the basement, though, so I wonder if it doesn't make more sense to just run an individual wire. Any thoughts on this?8.4.3
 
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Old 09-28-20, 05:32 PM
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My forum partner is the Redlink specialist. He would have offered the suggestion you arrived at.
Good decision.

I usually replace the thermostat cable or abandon it and install a new one. I don't like loose ends.
I would recommend running a single wire over using one of those add-a-wire modules.
 
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