Proper way to get a C-wire.

TheHeat

I could use some help flushing out a C-wire for some smart thermostats.
I have a radiant heating setup with 6 zone valves (4 older Honeywells and 2 Tacos from an addition prior to my moving in). There is also a Honeywell valve for an indirect hot water tank. They are all controlled off a Taco 4-zone controller as pictured: https://www.dropbox.com/sh/0i2zcbk94sokw1t/AACoytU5z15shwWUineUpF8Ya?dl=0&preview=20201024_210022.jpg
Current heating thermostats are two-wire (R and W), but there’s a green conductor as well that I’d like to re-purpose as the common.
The Honeywell valves all appear to gang together and tie to the Isolated End Switch. The newer Taco zone wires connect to the Zone 1 and Zone 2 thermostat and Zone 1 & 2 end switch connections.
Aside from the transformer in the valve controller box and anything that may exist at the boiler, there are two transformers mounted on the wall, also pictured: https://www.dropbox.com/sh/0i2zcbk94sokw1t/AACoytU5z15shwWUineUpF8Ya?dl=0&preview=20201117_212329.jpg. These appear generally wired to the Honeywell circuits. It is only the Honeywell zones I’m interested in converting to use smart stats.
I came across the Taco wiring guide, which shows a couple options for common wiring: https://www.dropbox.com/sh/0i2zcbk94sokw1t/AACoytU5z15shwWUineUpF8Ya?dl=0&preview=zone_control_wiring_diagram_1009.0_51.pdf. However, neither exactly reflects my scenario.
The zone valve diagram shows wiring to terminal 1 of the zone 1 end switch. Will this work given Zone 1 isn’t any of the zones I’m looking to have upgraded to smart stats? It also shows a 2-wire connection instead of Taco’s 3. I assume no way to connect to the isolated end switch instead?
The zone circulator diagram shows wiring to a connection point I’m not sure I have unless it means a transformer terminal. Is there some functionality here that would work?
I’ve heard mixed things about connecting to the transformers if not provided with a dedicated common. I imagine this would also apply to the wall-mounted transformers too?

The room: https://www.dropbox.com/sh/0i2zcbk94sokw1t/AACoytU5z15shwWUineUpF8Ya?dl=0&preview=20201117_212347.jpg

Thanks for reading. I appreciate any help you can lend.

Solid_Fuel_Man

The green can simply be landed on the C connection on the zone valve controller. 

R= constant 24 volts
W= call for heat
C= negative or common for the 24volts

TheHeat

Thanks! That...makes sense. Can I connect to any of the 4 C terminals? The tstats in need of a C aren't the ones that are wired into the R and W.

TheHeat

Solid_Fuel_Man said:

The green can simply be landed on the C connection on the zone valve controller. 

R= constant 24 volts
W= call for heat
C= negative or common for the 24volts

Thanks! That...makes sense. Can I connect to any of the 4 C terminals? The tstats in need of a C aren't the ones that are wired into the R and W.

Solid_Fuel_Man

The thermostats which you want to upgrade are controlling zone valves which are powered by one of those transformers on the wall in your picture?

TheHeat

Solid_Fuel_Man said:

The thermostats which you want to upgrade are controlling zone valves which are powered by one of those transformers on the wall in your picture?

Yes, that is correct.

Solid_Fuel_Man

Solid_Fuel_Man

This is what you need to do. 

Basically "C" is common to the transformer, valve, and now the thermostat. R is 24 volts straight from the transformer, and w is the call for heat (switch in the thermostat connects R and C when its cold). 

TheHeat

Solid_Fuel_Man said:

This is what you need to do. 

Basically "C" is common to the transformer, valve, and now the thermostat. R is 24 volts straight from the transformer, and w is the call for heat (switch in the thermostat connects R and C when its cold). 

Thanks Solid_Fuel_Man! Heating advice from northern Maine pro comes highly appreciated.

Solid_Fuel_Man

You are welcome!