How to switch form line voltage thermostat to low voltage

[JPride]

I need help on how to install a new smart thermostat. Current thermostat is 120v. I have a heat only system. Do I need a new low voltage transformer and relay and where in the circuit do these get added.

Thank you,
JP

 

[AC Power]

So your existing thermostat ONLY has two wires? No more? Either way, I will draw it out for you....but I need to know what you have presently in the stat?

 

[JPride]

Thank you.

yes, just two wires. Black and white.

 

[AC Power]

I forgot to ask in my original reply.....What type of smart stat are you planning on getting? NEST, Ecobee, ?

 

[JPride]

I was planning on the Amazon stat. I do not really need a smart stat for my system. Just looking for something programmable that I can control over Wi-Fi to keep the pets warm during cold snaps. I was also thinking to just settle for another 120v stat if this proves to difficult or expensive.

attached are images of stat and relay.
Thanks, AC

 

[JPride]

Looks like the system is set up as follows:
Load goes into a junction box
Out of that junction box
1 line to goes to emergency shut off switch
1 line to thermostat
1 line to the Aquastat

Out of the Aquastat
1 line to circulator pump
1 line to a relay box

Out of the relay box
1 line to the burner

 

[AC Power]

Ok, the pictures where of significant help. Your tracing the location/ID of the conductors was good too. Thank-You!

Unfortunately, for that thermostat, as you mentioned in your original post, you would in fact need a transformer and relay in/at your furnace location. I looked at NEST and Ecobee as well.....no go neither.

If you want, I can draw it out for you.....or, of course, you can go get another line voltage thermostat and be done with it.

 

[JPride]

Hi AC,

a drawing would be great. Thanks.
Just not sure where to splice this in and what wire type to run to the new stat.

 

[AC Power]

Ok, I'll draft it up in the next short while.

 

[AC Power]

I am drawing this up. I need one bit for information before I can draft this.

REASON: Some heating valves are "fail safe", that is, they fail open. So, in the case of a wiring failure (cable going to the valve is damaged), the valve fails OPEN, thus in heating as water is circulating through it's respective radiator.

I need to know if your heating system starts when the switchleg of the thermostat is energized OR de-energized?

You will need an extension cord for this. Please measure your two (2) wires for 120v-to-ground. Measure to ground in the extension cord, NOT the other conductor in the thermostat. The ground (in the extension cord) is the center lower U-shaped female port at the female end of the extension cord. You don't have a ground at the thermostat....hence, you've the extension cord so as to have a ground reference.

Tell me what happens to BOTH conductors when it's:
- Not heating....Is the black live? Is the white live? Both live?
- When heating...Is the black live? Is the white live? Both live?

You should use a meter for this, not an inductive no-contact "TICK" tester ("Google" it). REASON: "TICK" testers operate on the presence of induction, and they can produce horrible false-positives for results. I can use them, but a homeowner can get VERY confused by them for this application.

 

[JPride]

Thank you the comprehensive approach to this. Right now I can say that the system starts when contact is being made at the thermostat. When I turn up the temp the metal outer plate in the stat closes to make contact and turns everything on. Not sure this is of any help. I will have to further test to see when and which lines are being powered.

 

[AC Power]

Ok, well as you where able to explain it this well, that should be good enough. It appears your heating system starts (re-circ pump and burner) upon a CLOSED circuit (not fail-safe).

Let me draw this up....give me a few days.

 

[JPride]

Thank you. I really do appreciate you taking the time to assist me.

 

[AC Power]

Ok, you'll see I've drawn the wiring needed for a new t-stat (Amazon is fine, but it's regardless).

The drawing is fundamental / concept only.

You would need AT LEAST three conductors, but 5 conductor is standard procedure, that is, #18 AWG - 5-wires/conductors. (Your US Home Depot Cat # = Model# 210-1005BR )

You'll need a 120-to-24 vac transformer, 40mA minimum (Home Depot = Model #AT72D, Store SKU = 977267)
You'll need a 24vac relay c/w at least one set of C, NO, NC contacts (form C). (Model LY2 - AC24 at an electrical wholesalers).
You'll need your new t-stat of course.

 

[JPride]

This is great thanks for taking the time out to help a stranger. You even provided the part numbers for the items needed. I’m going to review the drawing and then give it a go when I get back to the house next weekend.

 

[AC Power]

Your Welcome....glad to help. It might appear daunting. I "pop in" to this website occasionally, so I'll notice if you have another question.