Just want a c-wire at my thermostat. 4 different HVAC techs have told me 4 different things.

heatwithmyboilerpls

Pics: https://imgur.com/a/oN7QMX8

I have oil heat using baseboard. There are 2 zones and 2 thermostats, one on the 1st floor and one on the 2nd. I had 4 different HVAC techs come out to give quotes on running a c-wire to the 1st floor thermostat so I could replace it with a smart thermostat and each gave me a different answer.

1) Just looked at the heater, mostly the zone valves(? the Taco things) and said it was super easy and that there's already a C-wire running to the 1st floor.

2) There's no C-wire but it should be possible if he installs a transformer

3) There's no C-wire but he gave 3 possible options.

- Install a transformer
- It might be possible to just run a C-wire from this thing
- Get an Ecobee (Pro I think) that has some adapter thing he can install on the heater.
-
4) There's no C-wire but he can run a relay between the zone valves.

Well, now I have no idea what I should do. Should I just call the first tech, since he thinks it should be easy? Worst case he would realize it's hard and have to go with one of the other options. I'm just afraid it means he doesn't know what he's doing so I should avoid him. Totally unfamiliar with any of this stuff so i'm clueless.

Any advice?

HVACNUT

Take the thermostats sub bases off the wall and see if there's a Green wire back there. There are some green wires at the Zone valves. If so, and if there's enough slack wire, you can use that as the Common.
Check out the Taco ZVC zone panels or equivalent if you want it done professionally. 

heatwithmyboilerpls

Been learning everything in the last few hours so I only have some basic understanding so if I say anything dumb that's why.

HVACNUT said:

Take the thermostats sub bases off the wall and see if there's a Green wire back there. There are some green wires at the Zone valves. If so, and if there's enough slack wire, you can use that as the Common.

If the green wire is there and has slack, does that just mean the other end of the green wire at the zone valve just needs to connect to the same terminal that the c-wire from transformer is connected to?

HVACNUT said:

Check out the Taco ZVC zone panels or equivalent if you want it done professionally. 

Sorry, not sure what this means. My plan is to call an HVAC tech no matter what because there's some other work I need done I didn't mention. I'm trying to understand which of the previous 4 HVAC techs I called was correct so I don't call back one who maybe doesn't know as much as the others.

HomerJSmith

Do as HVACNUT suggests first. Sometimes the green wire is wrapped around the cable in the wall and only the red and white wire is screwed on the thermostat back plate. lucky you if that is the case. That green wire is your C wire.Report back.

Jamie Hall

The reason you are getting four different responses is that sometimes it is easy -- and sometimes it's not, and it's not always possible to tell on the basis of a cursory inspection.

If, however, there is a green wire at the thermostat which isn't connected, and there is also a green wire at or near the zone valves, and if it is the same green wire at both ends, and if it isn't doing anything else, and if there is a common connection at or near the zone valves, and if the zone valve transformer has enough power -- then yes, it is easy.

heatwithmyboilerpls

@HVACNUT @Jamie Hall there is no 3rd wire at the thermostat

EBEBRATT-Ed

@heatwithmyboilerpls

You already have a 40 va transformer in the picture you posted so you have a common terminal you can connect to at the boiler. It is also available on your Taco valve(s)

That transformer is large enough to run 3 Taco valve....you have 2 so it SHOULD be fine. Worse case your tech installs a 50 va transformer in place of the one you have and runs a new 3 wire cable to the first floor stat. If I was doing it I would also add a Rib Relay they are small $$

EdTheHeaterMan

You have 2 problems to solve.
1. There are only 2 wires and you need to run an extra wire from the thermostat location to the boiler room/zone valve area.
2. Taco zone valves are not compatible with many smart thermostats because of the internal design of the actuator mechanism


Here is my explanation and solution.
https://forum.heatinghelp.com/discussion/comment/1706043#Comment_1706043
Look closely at the illustration. See the red box has a set of contacts that open when the element gets too hot. those open contacts break the circuit from Transformer R to the thermostat R to the thermostat W to the zone valve #1 to the zone valve #2 back to the transformer W . Some thermostats find this to be an error and will not work without an isolation relay

heatwithmyboilerpls

@EdTheHeaterMan thanks, though the diagram is way over my head. Question about the taco not being compatible. Isn’t the c wire just power and the other cables are the same? How are there issues

heatwithmyboilerpls

@EBEBRATT-Ed what is the relay for? Also, I’m trying to learn this as I go. For the new wire, would it typically be run directly from the transformer or from the taco or somewhere else?

EdTheHeaterMan

Basic electricity theory states that you need to have a SOURCE and a LOAD. a simple flash light has SOURCE the batteries and a LOAD the light bulb. You need to start from the SOURCE and go to the LOAD and have a return path back to the SOURCE. when that happens the light bulb will shine bright. if you break that path the light bulb will go out.

Here is a generator a switch that is closed and a light bulb. you can see the complete path form SOURCE to switch to LOAD and back to the SOURCE


In the case of the smart thermostat, the computer chip and circuit board inside the thermostat is the LOAD. the R wire comes from the SOURCE (a 24 volt transformer) and the C wire is the return path back to the SOURCE. The C Wire is not the power as you stated... it is the return path.

You do not need a return path (C wire) for a standard thermostat because it does not have a LOAD in it. It is just a switch that opens and closes based on the room temperature.

heatwithmyboilerpls

@EdTheHeaterMan got it. But I’m still confused how the taco wouldn’t be compatible with the smart thermostats. Don’t they behave the same way, they just need the extra cable?

EdTheHeaterMan

You may have a C wire that is not connected at the thermostat. it may be wrapped around the wire inside the wall.
That would be a good thing. You may still need the relay.

heatwithmyboilerpls

@EdTheHeaterMan that cable with the green wire is going from the transformer to the taco. The cable that goes from the taco to the thermostat only has the 2 wires (not sure what this all means though)

what is the relay for? Why is it needed instead of just running one cable from the taco (or transformer?) to the thermostat?

hot_rod

The Taco wiring options
https://forum.heatinghelp.com/discussion/186002/connecting-taco-controls-and-nest-thermostats#latest

heatwithmyboilerpls

@hot_rod Sorry, that threads entirely over my head. Whats the gist? Any actual issues or can I just run a new wire from the taco to my thermostat and just leave the other cables as is?

hot_rod

heatwithmyboilerpls said:

@hot_rod Sorry, that threads entirely over my head. Whats the gist? Any actual issues or can I just run a new wire from the taco to my thermostat and just leave the other cables as is?

I see it doesn’t cover your type of zone valves anyways.

Jamie Hall

The reason many of us prefer to use a relay with the power hungry smart thermostats is this. It separates the thermostat and its power source completely from the valves and other controls and their power sources. This makes wiring simpler -- and reduces the likelihood of getting out of phase or short circuit problems.

You use one power sourse -- a nice big 24 Vac transfromer -- to power the smart thermostats. The thermostats control the associated relays. The dry contacts on the relays, which are not connected electrically in any way to the thermostat power, provide the on/off switching which the valves and other heating control circuits need. The independent power avoids the rather common problem of the thermostats drawing more power than the valve controls can provide.

EBEBRATT-Ed

@heatwithmyboilerpls

Do you want to have this work the first time and be trouble free or possibly have issues?

If you want it to work use a rib relay as at least 3 of us have suggested and run a new 3 wire cable to the stat....done

heatwithmyboilerpls

@EBEBRATT-Ed I'm not trying to argue against a relay, i'm just trying to understand what work i'll be getting done in my house.

@Jamie Hall Thank you

EdTheHeaterMan

heatwithmyboilerpls said:

@EdTheHeaterMan that cable with the green wire is going from the transformer to the taco. The cable that goes from the taco to the thermostat only has the 2 wires (not sure what this all means though)

what is the relay for? Why is it needed instead of just running one cable from the taco (or transformer?) to the thermostat?

OK. lets take a step back.

Not everyone has a grasp on electricity and how it works. All they care about is that it works. Understanding how relays, transformers, capacitors and circuitry inside the thing do what they do, is not necessary in order to turn on a light switch.

The first step is to get 3 wires to the thermostat location. Then, connect what ever C wire thermostat @heatwithmyboilerpls has selected. The thermostat may work without the need for a relay. So let's stop with the what ifs. because... What if it works fine? Then we have confused the issue with information that is unnecessary. Just know it it does not work the wya you think it should, there are options.

I'm not sure that @heatwithmyboilerpls is actually going to do the work. He needs to find someone that understands how to do it. My suggestion is to make a deal with the contractor you select... If you can make it work then you will get paid. If you can't make it work then don't take the job. Hold 50% of the final payment until you are sure that it works for a week after the tech is finished. COD jobs will make sure that if it does not work, then the tech wont be back.

I hate to be so skeptical about our trade, but I have been the clean-up man too many times that "the last three guys could not get it fixed and I paid $XXXX.00 and it still don't work.". I offer to fix it right and tell them the price up front. let them think about it. Then take as small of a deposit as I can afford. A week or so later I check back with them and ask how it is doing. If it works then I ask them to mail me a check for the balance. If it is not working, then Im back to find out why. (that rarely happened by the way)

Good luck with your new thermostat. I hope you find someone you can trust to get the job done.

EdTheHeaterMan

Also. If you select a contractor that does not get it right the first time... He can always check in with us here to get help.
That is what we do.

@EBEBRATT-Ed I'm not trying to argue against a relay, i'm just trying to understand what work i'll be getting done in my house.

As far as what you may be getting into.
1. There will need to be a wire with 3 conductors run from the thermostat location to the boiler room. (or zone valve location) it can be another wire by it self or it can be a completely new wire with 3 or 4 or more conductors. (the conductors are the copper wires inside the different color insulation.)
2. You may or may not need a relay for the reason that Jamie sited
3. You may or may not need an additional transformer for the reason Jamie sited.

Be prepared for the mechanic to offer to try with out the added components. Then be prepared to pay a little extra to add those components as the job progresses.

Look at the manufacturers instructions for more than one option to make it work. You have zone valves... That is not the most common way to connect a thermostat. Less than 30% of heating systems in the USA are boilers (hot water). There are many more furnaces (Hot Air) that boilers. Out of all the boilers that are in the USA, not all of them use zone valves. So You have a rare condition that may take someone that is better than the average HVAC technician.

Good Luck with getting your new thermostat working.

HomerJSmith

This might help. You have to have a third wire from the thermostat.

heatwithmyboilerpls

@EdTheHeaterMan thanks for the replies, I really appreciate it!

Had another 2 techs come out to be safe and one suggested adding a relay and the other said just add the 3rd wire.

Are there any downsides to adding the relay? If I don't get one added and it turns out it was needed, will the result just be that the thermostat doesn't work or something potentially worse?

Also I followed up with the one who said no relay telling him someone else had suggested one and his response was "Running a wire should be enough. How do they plan to power the relay? The point of a relay is to keep 2 power sources separate. But the thermostat is being powered by the same transformer as the zone valves. So a relay isn't needed." Thoughts?

Jamie Hall

Your man who didn't know how to power the relay wasn't paying attention. The relay is powered by a second 24 VAC transformer which also powers the thermostats.

HomerJSmith

You need a relay because of the way that the 571's operate. It shuts off power to the heat motor coil wiring. See my post for relay connections. Go with the guy that says you need a relay. The TT boiler connection is powered by a boiler transformer that operates a relay in the boiler. Thus you have 2 transformers, a boiler transformer and an aux transformer. Count the transformers in Ed's diagram hint: (2).

The point of a relay is to keep 2 power sources separate

Ya!... The Aux transformer should have enough power to operate all the Wifi thermosats, relays, and the Zone Valves. You need an isolation relay for each Wifi thermostat. You need a isolation relay to charge the Wifi thermostat.

Ed The HeaterMan has explained this in another post. Again... why you need a relay.

EBEBRATT-Ed

I really don't know why people get twisted up with this. A relay and a second transformer will be the fix every time.

Is it worth the cost of more service calls to get this right? Or just put the relay and transformer in. For the price of the parts, it's not worth trying to make it work without them along with all the wasted time and head scratching

EdTheHeaterMan

EBEBRATT-Ed said:

I really don't know why people get twisted up with this. A relay and a second transformer will be the fix every time.

Is it worth the cost of more service calls to get this right? Or just put the relay and transformer in. For the price of the parts, it's not worth trying to make it work without them along with all the wasted time and head scratching

AGREE

But sometimes, in order to learn, we need to take it a step at a time. If you learned the only way to put an AC system in a home was to use a 2 stage compressor and 2 stages of resistance heat and a 4 stage heat 2 stage cooling thermostat for the 2 stage compressor with reversing valve, and multiple fan speeds, you might get a little overwhelmed at that wiring diagram. I know I was, but adding a fan center to a gas furnace was relatively simple back in the day.

Get the extra wire in place first. Then add the relay. Hope the thermostat didn't fail or the smoke come out of anything in the process

HomerJSmith

Don't believe me, I suffer from the Cassandra curse. Believe EBERATT-Ed and Ed Young, and other smart folk on this site.

AFOCT

I carry Fast-Stat Common maker on the van. Cheaper and faster than pulling a wire. Can be in and out in 35 mins. Why these are not in everyone's van I will never understand.

https://www.supplyhouse.com/Fast-Stat-FSCM00-Common-Maker-Thermostat-Wire-Extender-Adds-a-Common-C-Connection?gclid=CjwKCAiAh9qdBhAOEiwAvxIok0A7q-idGOCe3UN-rlqv9x-KcvQIoKFFBDQMdqDRCnaleY5jUjspkhoC91gQAvD_BwE