Installing wifi-smart thermostat with 2-3 wires hydronic heat-only

Cantdecide

Hi everyone! Newbie here 😀 desperately hoping someone can give some good advice & solutions on how to replace all (7) of our thermostats in the house that control control heat-only hydronic baseboard and hydronic radiant floor heaters. These are about 17 years old FYI.

I’ve been doing a lot of research and reading (this site is so resourceful!) and I realize not easy when there’s no C- wire that’s required to provide the voltage necessary to run the smart thermostats constantly. All thermostats only use 2 wires, but I did notice that most (not all! Why!? 😩) have an unused green wire hidden in the back.

I’m totally new to this, but with all my searching and reading, I found the switch relay boxes in the boiler room in the basement made by Argo (2 6-zone units - Model ARM 6-P). I do see some of those unused green wires also at the box (why would just a few be 2-wires instead of the 3?)

I found the “common” screw at the top right of the board - unused.

would I be able to successfully connect somehow the green unused wires (some are cut short FYI!) to the COMMON to use as the c-wires for the thermostats? Hoping the answer is yes, and hoping you can walk me through the steps.

and then for the couple that don’t have them extra wire, is it a lost cause?

ratio

https://www.supplyhouse.com/Fast-Stat-FSCM00-Common-Maker-Thermostat-Wire-Extender-Adds-a-Common-C-Connection

HVACNUT

6 va per thermostat.

Cantdecide

thanks both @ratio and @HVACNUT ! So I’m a total noob good student.

so seems for optimal operation I really do need to invest In the Isolation relay, regardless of whether I can connect those unused wires to the COMMON on the board? I was hoping if I just focus on the ones that actually had that 3rd wire, I could simply do COMMON connection and I’m set. Is that wrong?

if yes, is it Ok to “share” on do the Isolation Relays between both boxes, or is that asking for trouble?

also, what I’m confused about is do I still also need a transformer? And is it something like the one that @ratio linked above?

any chance anyone has any “real life” pics of how the setup should look?

ratio

In addition to providing isolation, the module @HVACNUT showed above provides power to the connected thermostats, by a separate transformer that's probably not included in the package. If you go this way, yes you can use the green wire as a common where it's available, & then use that add-a-common module on the few zones where you don't have an extra wire.

As for sharing the iso modules between the zone modules, shouldn't be any issue. I might break it up into two sets of six thermostats with a 50 VA xfrmr for each assembly (kinda like what's shown in the pic), or maybe just one 100 VA xfrmr for all of them together, depending on what I find in the back of the truck.

https://www.supplyhouse.com/Functional-Devices-TR50VA002-Transformer-50VA-120-to-24-Vac-Foot-and-Dual-Threaded-Hub-Mount

https://www.supplyhouse.com/Functional-Devices-TR100VA002-Transformer-w-Circuit-Breaker-Foot-Dual-Threaded-Hub-Mount-100VA-120-to-24-Vac

Cantdecide

really appreciate all the help @ratio its all starting to make more sense and I’m understanding how it’ll all work.

well. Seeing the 50VA transformer is out of stock until mid March thru mid April…is there any disadvantage to go the single big 100VA for both/all?

giess I can check out other sites, too.

EdTheHeaterMan

24 Volt transformers have different ratings that tell you how many accessories can be attached. The 24 VAC transformer that is on board the ARGO ARM6-P controls are not very powerful (only 30 VA). You may be able to use 2 WiFi thermostats using that transformer. I guarantee you that those transformers do not have enough power to supply 6 WiFi thermostats. Since ARGO makes the IR882 three isolation relay control, I would use them for all the zones that have the extra wire available.

When it comes to the thermostat wires that do not have the extra wire, I would take a closer look and peel back the outer insulation just a little farther to see if there is a wire that was cut off and then was recessed inside the outer cover. On those thermostats that do not have the third wire, you can use a device like this C wire Transformer and plug in to a wall outlet near the thermostat and just snake the wire inside the wall behind the thermostat with a wire coat hanger.

ratio

You should be fine with the 100VA xfrmr, I've used them plenty in the past.

You should do a sanity test to make sure it's adequate for the new thermostats though. Get the manual for whatever you're considering, & look through it for how many VA or amps it draws. Multiply that number by twelve stats, the xfrmr should be somewhat larger than that number. (VA, literally volt amperes, is used just like watts but for AC. If they only list amps (or milliamps), it's a simple conversion.) Do make sure you're reading its internal consumption, not the load rating.

Cantdecide

https://forum.heatinghelp.com/discussion/comment/1843533#Comment_1843533

Thank you! But why multiply by 12? Would t I be multiplying by 6, assuming I’ll have to use 2 IR882 ISO Relays (3 zones ea) + Transformer for 6 new thermostats?

and sorry for the basic question but want to make sure I don’t make any mistakes! I’ve been studying the drawings for the setup. For the wire types, I’ve read than the minimum to connect to the ARM 6P and ISO relay is 14G.

For my understanding, the wire though that connects the thermostats is 18G. Is this correct & OK? Or does this mean that the thermostat wire also needs to be 14G? I feel like the ones there are thinner than 14.

ratio

Multiply by the number of stats to get the full load. It looks from the picture that you can gang more than two of the isolation modules together, that's what I figured you meant about "sharing the iso modules". There's certainly no harm in two sets of modules, one set per zone controller. In fact, there may be a limit on how many you can gang together, so check on that too.

18 gauge will be fine.

Cantdecide

so I just have been wanting to test a 3-wire setup for 1 of the thermostats that had the hidden inside green. I found the matching zone on the ARGO panel - connected the green wire to Common and it’s not working.

does something need to be connected to the 24V port?

EdTheHeaterMan

You need to reverse the Red and White wires

The red wire is on Tw. and the white wire is on TR. This makes no difference when there is only 2 wires. But it makes a difference when you have 3 wires and one of them is common.

Look close at the red and white wires on the zone 6 label. The left is for the White to W on the thermostat. The right one TR must be connected to R.

Cantdecide

https://forum.heatinghelp.com/discussion/comment/1846459#Comment_1846459

So good to know that when it’s 2-wires it doesnt matter but 3 wires matters.

i switch them and it’s still not working. There’s no power drawing to the ecobee thermostat. Is there something else that is missing?

or do I have to wait now for all those parts to arrive (I ordered the IR-882 Isolation Relay)

Here’s the wiring at the thermostat

EdTheHeaterMan

Just so you know. The R that your arrow is pointed to is connected to the TR on all the zones from behind the printed circuit board. That way all the thermostat R terminals are properly connected to the 24 V transformer properly.

Cantdecide

To be clear, I haven’t added anything else to the board circuitry…meaning, no “power” to the 24V point just under the Common.

this board is the 2nd one in the setup…not sure if that matters?

but super bummed that nothing is working or turning on at the thermostat. Not sure what I’m doing wrong 😞

ratio

100% sure you got the right zone?

The spare green might be broken somewhere, this occasionally happens if the wire gets extended.

If you have a meter, check for ≈24 VAC (22ish-27ish) between the green & red wires.

Cantdecide

@ratio i mean…I’m like 99.9% sure. Unfortunately, I had bought a meter but misplaced it 😞

Just to be sure, I just tried another zone. And same thing. Ecobee is not powering up.

perhaps it’s not enough power just with the existing boards. I’ll try again once the IRs come and the transformers. I’m hoping it’s just that.

And perhaps in the mean time I should order another volt meter!

Cantdecide

TR100VA004

TR100VA002

Also what’s the difference between these? Will either work or are they very different & then which one only can I use?

EdTheHeaterMan

Try putting the Red wire on Rc at the thermostat

Rh is for when you have two different units, like an air conditioner and a boiler connected, so the R wires form both systems can stay separate. You only have one system with a transformer

The thermostat is powered by Rc and C

ratio

https://forum.heatinghelp.com/discussion/comment/1846519#Comment_1846519

TR100VA004 is a multi-tap (480/277/240/120 volt) primary 24 volt secondary, TR100VA002 is a single-tap 120 volt primary, Other than that, they're identical. You should be able to use either one, be sure to cap off the unused primary taps individually if you use the 004.

Cantdecide

https://forum.heatinghelp.com/discussion/comment/1846531#Comment_1846531

OMG!! You’re a life saver! It worked!!! Woohoo! I’m so happy!

so so so so happy! Thank you for sticking with me!!!

I know I’ll be back thought, once the IRs and the transformers arrive and I find the time to set those all up!!! But I’m psyched.

Cantdecide

https://forum.heatinghelp.com/discussion/comment/1843533#Comment_1843533

ok so circling back in the required VA for the transformer. I’m confused.

Although I have 11 zones, not all need the extra VA to operate correctly.

3 have the C-wires and are AC & Heat and these have been running perfectly for a few yrs

The rest are the ones I’m trying to figure out:

6 - have the unused 3rd green wire which can be used as COMMON (like in my test unit today)

2 have no 3rd wire and only 2 wires - I will have to get those Fast Stat thing that @ratio suggested above

so from a required VA for the transformer, do I still have to calculate for 11 thermostats? I’m googling, it seems Ecobee says each thermostat draws 3.5-5 A. How do I calculate the VA if I don’t know the PF? In a Reddit post someone said it’s 3.5VA per thermostat so then do I still need 11x3.5=38.5 (so 100VA is way overkill)

but I’m wondering is it just 8 units x 3.5 that I need to calculate since the 3 have the “official C-wire” already?

pls help me understand thanks!

ratio

Regarding the ecobee, ISTR 3.5VA as well, but that sounds lowish to me if they're WiFi. That 3.5-5A isn't very believable—but I suppose it's possible as a momentary peak when the radio transmits. Probably that 3.5VA is averaged over some time and includes an average amount of radio transmissions.

Are you using the ARM relay module to isolate & power the ecobees? If so, you'll need to provide power for every one that's attached to it/them. 8 stats = 8*3.5VA = 28VA at a minimum. Are the other stats going to stay directly connected to the zone panel (with or without the common extender)? If so, you won't need to account for them with the new transformer. If they're going to be attached to the ARM, then you'll need to account for them as well: cal it 40VA.

Since these are smart WiFI stats, I wouldn't go in to it with less than 50 VA, to give you some headroom if several stats decide to start transmitting at once. You can get away with something smaller than the 100VA if you wanted to, but those 100VA models have a circuit breaker on the output, which is nice to have. You'll have to check & see if the 50VA model has a circuit breaker, not all do at that size (some have internal fuses, which is no bueno).

EdTheHeaterMan

@Cantdecide said: (what is in bold) My response (is in regular font)

3 have the C-wires and are AC & Heat and these have been running perfectly for a few yrs   These do not need to be added to the new transformer

The rest are the ones I’m trying to figure out:

6 - have the unused 3rd green wire which can be used as COMMON (like in my test unit today)  These 6 are what you need to have enough power for (power = VA) and the transformer needs to power the thermostats and the relay that the thermostat operates. So I believe a 50 VA can do all 6, but if they are not all on the same Zone Relay, then you might want to split them up with separate transformers per zone relay and I would use 40 VA with up to 4 thermostats and the associated relay.

2 have no 3rd wire and only 2 wires - I will have to get those Fast Stat thing that @ratio suggested above.  These two need to have two separate add-on transformers that can be added right at the thermostat by plugging it into a wall outlet near the thermostat and running the wire up to the thermostat locally. this is where you would use the Rc and C for the add on transformer and use the Rh and W for the call for heat. You will be using two power sources on these two thermostats.

EBEBRATT-Ed

You need to find out how many amps or VA the thermostat uses.

3.5-5 amps cannot be right

3.5-5 VA could be right

If Ecobee gives you the thermostat power in amps then take the amps given (call that X)

x times 24(the system voltage) will give you the rating in VA

I looked quicky on line and could not find that information.

tcassano87

https://forum.heatinghelp.com/discussion/comment/1843457#Comment_1843457

can that be used with a taco switch relay as well for the same application?

Cantdecide

https://forum.heatinghelp.com/discussion/comment/1846604#Comment_1846604

ok yes. Perhaps it’s 3.5-5V 😀

I did find this post from someone who measure it:

“I power my Ecobee with a 24VAC wall-wort and it reads 1.9-2.1W on my Kill-a-Watt.”

Ok so another question. One of the thermostats that does NOT have the extra green wire is perhaps the highest on the priority list as it’s a room that is always used & heat is consistently used during cold months. The location of the 2nd floor room is vertically stacked on top of the boiler room that is in the basement. I noticed in the wall. The wires are pulled through a metal conduit. My dream is really to pull new wiring here… what are the chances I can manage to do this? I’ve read you use the existing wire as the fishing tool…

I want to try but I’m afraid. And also afraid of the difficulty and potential for failure…especially if then I have trouble getting the original wire back in place 😱

(I really don’t like the look of using a plug-in adapter for the power, so that is really not a route I’m considering)

any advice from experience? I’ve never fished wire long distances and between floors. But I’m a tenacious and excellent student. ☺️

ETA ok forget it. I disconnected wires at both ends and tried to start pulling. Definitely it’s not moving and afraid to pull harder for fear of damaging anything. Ok - back to the Fast Track device approach.