So I decided to install a smart thermostat. My house did not have a c-wire and I have a heat only system.
Some things to go over that if you don’t have a background in HVAC won’t make sense but once you read it does. Working IT we have the same kind of issue with acronyms that don’t translate well into normal speak.
- TSTAT is just short for Thermostat – I don’t know why it took so long for me to get this.
- c-wire means common wire this is essentially constant power source similar to the rc or rh but not switched.
- The terminals on your boiler and tstat
- RC is Red Cooling – this basicly means its a switched hot wire
- RH is Red Heat – this basucly means its a switched hot wire
- C Common – this is a constant on hot wire
- W is the return path or if you are familiar with electrical this is your neutral
So I had 2 options, run a special power extender kit which would have looked really clunky because I have 4 zones and would have needed to mount 4 power extenders or install an step down transformer and an isolation relay which I thought was overkill.
I found that I had a 3 wire cable run, Red White and Green. Green was not connected to the thermostat or the controller on the boiler. Green is generally for the fan, which I don’t have it being a boiler and not forced hot air.
I tried doing some research but there was much confusion including on Ecobee website that says you need a transformer and an isolation relay. This is the case only if do not have a 3rd wire you can use as your common.
So where do you plug in this third wire? There was a lot of confusion when looking this up because TACO in order to have a less complex system decided not to put a dedicated common on each zone tstat terminal and instead decided to do a single common which can be used on all 4 zones. Even more confusion came when people tried to connect the wires to the 24VAC terminal on the left and it didn’t work for reasons I won’t get into here.
See the terminal with COM near it? That’s where you common wires go. Not all boards say that and on some of them it is placed differently.