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I've read a hundred questions on this, and most of the answers come down to solutions I've tried that don't work, hiring an electrician, or doing some very messy work. I'm hoping there's some way to simplify things.

Here's what I'm dealing with:

  • A 3-zone heating system: Basement, Ground Floor, and Second Floor. Gas boiler is in the basement. Zones each have their own thermostat. Baseboard hydronic heating.
  • 2 wires controlling each t-stat. No C Wire. :-(
  • Ground Floor has an older Nest, with enough battery backup it hasn't run into issues
  • Basement and Second Floor have basic cheap t-stats
  • I bought two Ecobee 3s before I understood all of this, months ago. Now, after months of learning, I'm not seeing an easy solution, just a bunch of messy ones.
  • I can buy Nest 2020 t-stats, but they're unreliable without a C Wire, and have lousy battery backups. I want to get a C Wire, do this right. I'm not leaving this house until I die.
  • Basement wiring is loose. I can pull the cable right through and hook up a 3 or 5 wire setup, easy. I've found where the C wire would connect to. All good.

The Second Floor is where all the problems are happening. The cable is not loose. Based on what I've read, it's likely stapled to the studs or to something somewhere. :-( Fishing isn't an option here. Every answer I've read says I'm not going to be able to successfully pull those staples out.

I don't have ductwork I could run it through. The ducts come from the attic and go everywhere except the basement :-(

The basement has a finished ceiling, not a drop ceiling. :-( The attic is mostly finished, and I don't see any wiring up there that would provide a guide on how to get down 3 floors, but I'm exploring.

So, what haven't I thought of? I could rip off the baseboards, make a clean hole to get from Floor 2 to Floor 1, but that won't get the wire across the basement ceiling. I could pull up the hardwood floor on Floor 1 to get across, but that sounds messy. I could try running cable up to the attic and look for a straight shot down from there, but I doubt it exists. I could borrow/rent a thermal camera, look for where things are running in the walls, and try to find the cleanest route to run things before I start making holes, and, if I'm lucky, find a simple shot.

Anything I'm not considering? I see a relay that lets you connect a 5-wire t-stat to a 2 wire boiler by sitting in between and handling the messy stuff, but, of course, that's not what I need. If there were a relay that could stand between the t-stat and the boiler, sending power on one line and signal on another, and then send the proper two wires from itself, that would be great, but I'm not seeing such a product.

This is driving me nuts. I'm really trying to avoid driving the wife nuts by breaking up walls and/or floors everywhere, or spending hundreds just to run a wire, but I'm not seeing a third option.

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    I assume you don't want to run the wire on the outside of the house. – Platinum Goose Mar 2 at 4:05
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    Third option - nice dumb unhackable thermostats. I run wires for a living, sometimes it's just messy and involves a lot of drywall repair. Sometimes the allure of smart thermostats may not measure up to not having to repair a lot of drywall. Sometimes you can confine most of the drywall work to the inside of closets, where the paintjob does not have to be perfect, or is at least smaller if it does have to be perfect. – Ecnerwal Mar 2 at 4:10
  • does the furnace have a chimney? where is your vent stack is there anything that goes from basement to attic that you might be able to squeeze a wire beside – Jasen Mar 2 at 9:56
  • I ran a second sensor to our second floor by using blue jean thread, tied to a blown up zip lock bag, through the return air. Turned on the air handler and it got caught by the filter. Pulled the wire up from there. – Evil Elf Mar 2 at 12:52
  • I have never looked into smart thermostats, so I may be wrong. But I assume there might be options out there that would be more of a 2 piece setup. Thermostat is only powered through the existing 2 wires, and transmits the heating calls wirelessly to a receiver unit that is located at the boiler. Not sure if it exists, but might be worth researching. Or you could probably build something like it to retrofit the thermostats you have with a couple of Arduinos. – PhilippNagel Mar 2 at 14:07
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assuming you can't sneak the wire in beside a flue or a drain/vent stack. and don't want to install a new wire on the outside of your house.

Install a 24V transformer near where you need to power the thermostat and run bell wire from the transformer to the thermostats R/Rh and C terminals.

it could be a hard-wired doorbell transformer, or a plug in one.

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Turns out there was an option I hadn't considered! I can run the wires from the AC unit in the attic to the thermostat on the 2nd floor.

Basically, right now, it's:

  • Central AC unit in attic connected via 5 wires to a wireless Redlink unit
  • AC Wireless Redlink t-stat on 2nd floor (I hate this and was planning to find a better solution)
  • Heat t-stat on 2nd floor connected to boiler in basement via insufficient wiring
  • Boiler in basement

Instead of adding more wiring to get to the heat, going through the mess of getting to the basement, I can just run the wiring to the attic, using the AC in the attic for power, and gaining the ability to control my AC via the t-stat as well!

So I'll be running 7 wires into the Ecobee - 5 from the AC in the attic, and the 2 existing from the boiler in the basement. And there's easy ductwork going to the attic just feet above the heat t-stat, so connecting it is easy.

Let me know what you think, and I'll report back as I connect it.

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  • I think you have yourself an answer, that's what! – ThreePhaseEel Mar 3 at 3:47
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You could make the zone thermostats powered by the 2 wire and then have them communicate wirelessly to a module at your furnace which then switches the respective zones.

Using wireless zone thermostats you should be able to do the wireless communication, though I'm unsure if they support being charged from the low voltage wires or if they are only set to only be powered/charged by a wall wart.

A diy solution would work but that is beyond the scope of this SE.

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  • That sounds perfect! Where can I read more on such a module and how to set it up? – user3310972 Mar 2 at 16:05
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Solutions to consider

A. From outlet near thermostat use a 3V (or whatever is called for) wall wart wired to the thermostat battery terminals. You can run the low voltage wire along a baseboard and vertically through the wall.

B. For upstairs and attic ones if you can route new wire to crawl space you can exit through soffit, down outside behind rain downspout and in through basement window.

C. Hire a security system installer to do it. Please consider this. They are very very good at the particular techniques of fishing low voltage wire to every door and window without causing a lot of damage. I've seen them work magic. They use different routes, techniques and tools than electricians. They have skill and experience that you don't and that you never will if these two wires are the only ones you ever need as you grow old in this house. My suggestion "B" is an amateur trick they would never resort to.

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  • But doesn't option C mean "spending hundreds just to run a wire", which the OP explicitly does not want? Or just how cheap can hiring these pros be? – TooTea Mar 2 at 16:20
  • @TooTea OP's primary constraint was to retain his sanity, as expressed in the question. I don't think I addressed that very well. The cost consideration came very last. That's why I made it C not A but you're right, it will cost hundreds, not tens. I also withheld my (D): do you really need a smart thermostat for your main residence? Isn't a $30 programmable one good enough considering you are generally inside the house? – jay613 Mar 2 at 19:02

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