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Nest HVAC Upgrade Advice Wanted

Hi. I'm renting a house for the year and would like to explore upgrading the thermostats so we can have wifi control. The owners will pay for the equipment and I’ll volunteer the labor as long as it’s all doable by a handy layperson. I'll describe what they have and would appreciate your letting me know what you would recommend (or what questions you have). Thank you in advance!

The house is single family, 3 floors in different sections that were added on over the years. No attic or basement, but there is a crawl space below the living room.

Here’s a breakdown of the HVAC:

Ground Level (Living room, kitchen, dining room, laundry room):
The laundry room has a Weil-McLean oil furnace. On the furnace is an Argo ARM 861-3 control panel with an extra zone module for the adjacent hot water heater.
There is a First Co. 24HBXB-HW heat pump in the crawl space below the living room. I didn’t crawl in there to see the control panel, but it’s probably an EWC.
Living Room: Nest thermostat (let’s call this stat #1) controls zone 1 on the boiler which heats/cools all ground floor rooms. The Nest has W1-C-Rh-Y1-G and seems to work fine.

Bedrooms (two floors):
Honeywell TH3110D1008 (stat #2) battery powered in 2nd floor bedroom with W-Y-G-O-Rc (jumpered to R)-B. No C.
Honeywell T8775C1005 (stat #3) on 3rd floor with W-Y-R. This seems to be a slave to stat #2 for power.
These are both wired to an EWC-ST-3E panel next to a third floor heat pump. There are a couple of motorized dampers. It would be very challenging to run new wires to these stats.

Media Room and spare bedroom:
Nest for 2nd floor media room (stat #4) has C-W1-Y1-G-O-Rc and works fine.
Nest for 3rd floor bedroom (stat #5) has C-W1-Y1-Rc has no power even though there is a C wire to the panel. If there’s something wrong with the wire, I can replace this one fairly easily.
These are both wired to an EWC-ST-2E panel near the second floor heat pump. There are a couple of motorized dampers.


I would like to get all the zones on wifi so I can turn them on/off when not home. Having them all with Nests would be easiest since there are already three in place.

I see Google makes a $25 C-wire adapter:


Would getting two of these allow me to replace the Honeywells with Nests? Or do I also need to replace the control panels? And why would stat #5 not have power? I will dig out my multimeter but wonder if there’s an obvious reason like that older EWC board doesn’t provide power to a smart stat.

I would appreciate any advice you can share!



  • HomerJSmith
    HomerJSmith Member Posts: 2,509
    Nests do have a current draw. Make sure that the transformer can handle the total draw.
    EBEBRATT-Ed Member Posts: 15,827
    Nest need a lot of power to charge the internal battery. They work a lot better with a "C" wire.

    We get Nest posts on here daily. Most technicians hate them. Some of these stats are so expensive you can hardly recoop the cost of the energy saved if any
  • SuperTech
    SuperTech Member Posts: 2,205
    You will need to replace that old master/slave zone control board to use WiFi thermostats. I like to use the EWC NCM300. I would recommend using any other thermostat than the Nest. Those thermostats are over rated junk in my opinion.