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.