Want to replace my old thermostat with an Ecobee. Do I need a transformer/relay added to boiler?

heatwithmyboilerpls

I've had a few different HVAC techs come give me a quote and every single one has told me something different needed to be done and with wildly varying quotes. I'm not looking to do any of this work myself, I'm just trying to figure out which HVAC tech is correct so I can hire the right person.

I have oil heat using baseboard. There are 2 zones and 2 thermostats, one on the 1st floor and one on the 2nd. I'm only trying to replace the thermostat on the 1st floor. The old thermostat only has 2 wires running to it so it looks like I need to run a common wire from the boiler to the thermostat.

Pics of a bit of everything: https://imgur.com/a/RJSSV73

Pics mostly of aquastat(?): https://imgur.com/a/CPLM8Yn

Pics of zone valves: https://imgur.com/a/bPO755N



I've mostly been told 4 different things:

1. I can just run a wire from the boiler to the thermostat
1. I need to install a new transformer before running the wire
1. I need to install an isolation relay before running the wire
1. I need to install a new transformer and an isolation relay before running the wire

I have no idea which one is correct. Any advice?

Jamie Hall

Chances are very good that option 1 will work -- but you'll need to find the correct place to attach that one wire.

heatwithmyboilerpls

@Jamie Hall is there an easy way to confirm? Is it something an HVAC tech should have been able to confirm while giving a quote or would they need to do it once they're here to do the actual work?

Jamie Hall

heatwithmyboilerpls said:

@Jamie Hall is there an easy way to confirm? Is it something an HVAC tech should have been able to confirm while giving a quote or would they need to do it once they're here to do the actual work?

They'll need to look at it.

heatwithmyboilerpls

@Jamie Hall Sorry, to clarify do you mean they'd have to give it a cursory glance or actually take time to look at it? Trying to understand if the person who told me i'd need a transformer might discover I wouldn't need one when they got here or if they've already decided I need one just from when they took a quick look during the quote

EdTheHeaterMan

one ecobee gets connected to one zone valve. The rest of the controls are not effected. The zone valve end switch ISOLATES the thermostat from the rest of the system.


a. If you do not have this exact wiring then you will need a transformer and isolation relay.

b. If you have a problem with this wiring, it is because of the unique way that the Taco zone valve operates. I believe ecobee will work this way but if it has error "No power to R terminal" then you will need an isolation relay and a separate transformer because you are getting near the zone valve transformer's capacity with three zone valves there.

MikeAmann

Finally, someone actually asked the question FIRST, instead of the usual, "I bought a NEST. What do I do now?"

EdTheHeaterMan

If you are connecting more than one Ecobee thermostat then you will need a second transformer and isolation relays for each Ecobee.

heatwithmyboilerpls

@EdTheHeaterMan The 2nd Ecobee (on the 2nd floor) will get the common wire from the central AC in the attic. So one thermostat, the first floor, getting a c-wire from the boiler.

So for 1 thermostat do I need only the relay? How would the HVAC tech confirm?

Tim McElwain

All this confusion because millions were killed by two wire T87 thermostats with a mercury bulb. The truth is the small amount of mercury in that thermostat is way below the national danger level. However millions dropped dead in their homes because of T87's. Sorry just being sarcastic!!!

HomerJSmith

Here--try this. I already think you have a third wire wrapped around the cable to the thermostat.
Isolation relay-need one for each thermostat
https://www.supplyhouse.com/Jard-92290-SPST-24V-General-Purpose-Switching-Relay
Aux transformer
https: https://www.supplyhouse.com/Packard-PM12040-Class-ll-Plate-Mounted-120V-Input-24V-Output-40VA-Transformer

EBEBRATT-Ed

@heatwithmyboilerpls

You should not need a separate transformer and relay because 1 Ecobee is off your ac system which is a completely different system from your boiler which will have the second Ecobee if I am understanding your system right.

But (and it's up to you and your technician) I always recommend a separate transformer and relay for any "smart " thermostat. Why?:

because it will always work with no issues
the added parts are cheap.
you reduce any call backs about troublesome operation.
It just eliminates most all problem issues. such as

small or underpowered transformers.
Backfeeds to other controls

see the attached diagram for a Nest Thermostat.... pretty much the same thing. The wire marked boiler control circuit would go to your Taco valve

HomerJSmith

1. I can just run a wire from the boiler to the thermostat--NO
1. I need to install a new transformer before running the wire--YES
1. I need to install an isolation relay before running the wire--YES
1. I need to install a new transformer and an isolation relay before running the wire--YES, YES, YES

heatwithmyboilerpls

@HomerJSmith @EBEBRATT-Ed @EdTheHeaterMan

So sound like new transformer + relay is the correct way to go. I actually had multiple techs suggest just the transformer. If I ask one of them to also add a relay, is there anything specific I should tell them so that they add the correct kind of relay?

EdTheHeaterMan

This part has both the relay and the transformer all in one convenient part. https://www.supplyhouse.com/Resideo-R8285A1048-40-VA-Fan-Center-w-SPDT-Switch-Includes-R8222B.

It is less money that purchasing the transformer and the RIB-relay separately. Here is the diagramThe above illustration was edited from the illustration in the I/O sheet that comes with the part.



And i agree with Homer's statement just below this post if you purchase the RIB relay. If you go with the R8285A Relay/Transformer for the economy (only a few dollars) then the diagram above has identical wire connections. The colors are just different, but electricity is colorblind and "the names have been changed to protect the innocent."

HomerJSmith

The reason that you can't use the aquastat transformer is because you can't make a connection to the transformer common beside which you have more than one thermostat you need that for the non wifi thermostat. Taco ZVs 571 presents their own problems which is why you need a isolation relay.

I think you would have a success with my diagram. Show it to your tech and get his opinion.