Nest Thermostat With Gas Fireplace (or Other Millivolt System)

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Introduction: Nest Thermostat With Gas Fireplace (or Other Millivolt System)

About: I would rather learn how to do it myself rather than pay someone else to do it for me.

This short tutorial will help you use your Nest thermostat with your gas fireplace or other millivolt type system. I found some other tutorials online but none really seemed to cover everything you'll need so here you go!

Step 1: Purchase a 24v AC Adapter

Your gas fireplace or other millivolt system does not operate using 24v AC like most HVAC systems. You have to supply the 24v using an external transformer. I got mine at Lowes for $7.99 (item number 168261).

Step 2: Purchase a Fan Relay

You will need a fan relay. I got mine at Grainger for $9.05 (item number 1N184). The Nest is going to switch the 24v source and this relay is going to switch the millivolt system in your gas fireplace.

Step 3: Install the Nest and Connect the Wiring

First, disconnect the thermostat wires from the gas fireplace -- you will use your existing thermostat wiring -- and it's always a good idea to disconnect things when working with electricity. Install the AC adapter -- I placed mine behind the wall in the laundry room (very convenient there was an outlet right there for me) and ran the wiring up the wall and through the same hole as the thermostat wire.

Connect one lead from the AC adapter to the RH terminal on the Nest backplate (you will probably have to tin the end of the wire so the Nest can sense there is a wire connected), splice the other lead from the AC adapter to the existing RED thermostat wire and finally the WHITE thermostat wire to the W1 terminal on the Nest backplate.

Step 4: Connect the Relay

Install the relay in or near the gas fireplace. You may need to have some female spade terminals handy for this step if you don't already have them. Put those on all the wires -- two wires from the Nest and the two wires in the fireplace -- first if needed.

Connect your existing thermostat wires from the Nest to terminals 1 and 3 on the relay. Connect the thermostat leads from the fireplace to terminals 2 and 4 on the relay.

Step 5: Plug in the AC Adapter and Connect the Nest

Plug in the AC adapter. Connect the Nest thermostat to the backplate.

If all is well, you should now have a fully functional Nest thermostat to operate your gas fireplace. It took a while to fully charge the battery in the Nest so that I could configure the WiFi network settings and access the thermostat from the app.

6 People Made This Project!

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150 Comments

0
corruptfile
corruptfile

Question 15 days ago

How does the 24VAC transformer charge the Nest and control the relay. The only way the 24 VAC circuit to the Nest is complete is when the coil in the relay sees power, which will turn on the heat. So it only charges during heat cycles? What happens when there is no heating?

0
msenn77
msenn77

Answer 15 days ago

Long answer: I don't know how the Nest manages to do it either. As far as the Nest is concerned this setup is no different than connecting it to a heating appliance that provides 24VAC its control board directly. This setup has been running in my home without issue since this tutorial was posted almost four years ago.

Short answer: Magic

0
hebertnhjth
hebertnhjth

Question 4 weeks ago on Step 5

I have aTaco SR506 relay system for me forced hot water heat. There are 3 milivolt thermostats connected to the system. Can I use this solution with that Taco SR506?

0
msenn77
msenn77

Answer 4 weeks ago

I'm not familiar with this and after a quick Google search I'm struggling to find a manual anywhere for the Taco SR506. I do see in a few of the images that there appears to be a 24VAC output terminal on the board (refer to the image I've attached). Is this correct? Or, do you have 24VAC at the thermostat terminals? If the former is the case it could probably be wired slightly differently to provide 24VAC over the thermostat wiring to charge/power the Nest. If the latter is the case I believe the thermostat terminals would provide the necessary 24VAC to charge/power the Nest as would be the case in a "traditional" (non-millivolt) setup. If the Taco SR506 really is a millivolt system then yes, I believe that you could use my instructions here to add one Nest for each Zone connection or when wired in parallel one Nest could probably be used to turn on or off all zones simultaneously. The moral of the story here, though, is that I don't know enough about the Taco SR506 to be absolutely sure of whether it would work or not as outlined here or with minor modifications.

Taco_SR506.png
0
DanielO4
DanielO4

3 months ago

I'm placing this nest below the one that controls my furnace, can I just piggyback the C and Rh from the furnace nest instead of using a 24V adapter?

0
DanielO4
DanielO4

Reply 3 months ago

In answer to my own question, yes you can. I brought up the C and Rh from the furnace and tied it together and wired it up as gantho diagramed below. Works great. To be specific though, Rh from furnace to Nest Rh. C from furnace split to go to Nest C and down to switch. W1 from Nest down to the switch.

0
msenn77
msenn77

Reply 2 months ago

I'm glad you were able to get it figured out. I'm usually much better about replying but I've been out of town and didn't see either message until just now.

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Thom Strom
Thom Strom

7 months ago

I just wanted to send my thanks. I followed this recipe to a tee, and it worked brilliantly to adapt an antique furnace from 1951 to a Nest thermostat. In particular, I wanted to call out your hint to tin the end of the wire so that the Nest would detect power properly.

0
msenn77
msenn77

Reply 7 months ago

You're welcome. I'm glad it worked for you!

0
bobr243
bobr243

9 months ago

I have a Mendota gas fireplace that has a Smart-Stat-II remote. It connects to a Mendota Thermostat that has a fan control.

I had originally wired up a Nest E up without the relay using instructions I found on YouTube. That worked for days but the fireplace started to make a ticking sound.

So I figured that I needed the relay and followed these instructions and it works for a short period of time before the power adapter fails; I've killed two now. After using it, Nest reports that there isn't any power (R).
The black wires going to the Nest in the picture are the power adapter, R and C.
I have a White Rodgers 90-370 Relay. 2 & 4 going to the fireplace thermostat.
3 goes to W1 on the Nest
1 goes to C along with the power adapter.

The first time I tried I was cleaning everything up and I briefly touched the power supply wires together and figured I killed it. I purchased a second one and was extremely careful this time and after a few tries turning on the fireplace, the Nest again reported there was no power - R.

nest3.jpgboth.jpgSSII.jpegThermo.jpegrelay.jpg
0
msenn77
msenn77

Reply 9 months ago

Can you take a picture of your power adapter? Also, You may need to tin the ends of the wires. I found because the wires from the power adapter were such a small gauge and stranded that they weren't making good contact in the base of the Nest. Let me know...

0
bobr243
bobr243

Reply 9 months ago

I have to take most of the fireplace apart to see the connections. If you look at the Thermostat the Red connection goes to TH and the Black goes to TPTH. Should I connect 2 and 4 on the relay to TH and TPTH? Does it matter where 2 & 4 connect to?

wires1.jpegwires2.jpeg
0
msenn77
msenn77

Reply 8 months ago

It should not matter as you are only connecting the circuit between those two terminals.

0
bobr243
bobr243

Reply 9 months ago

I believe I have it working now. I purchased a Venstar ACC0436 2-Wire Kit and used that relay and power supply and it seems to be working. The instruction look to be identical to what is detailed here. The relay is also silent. Thanks for posting this and the help.

Venstar.jpegVenstar_Manual.jpg
0
COBRAGUY42
COBRAGUY42

Question 11 months ago

Thanks a million for the tutorial. I've been using this successfully for 2 years at my cottage. Before I leave the house i turn up the heat via the app.

For some reason whenever I'm at the cottage there are times when the nest doesn't have enough power to keep the wifi connection. (Not sure why it's only when I'm there, possibly the display coming on and off is just enough draw) I used the adapter you cited but I'm wondering if I need to hook it up differently or use a better adapter. I really don't want the nest going dead when I'm not there as I keep it at 10c and I don't want the place to freeze.

0
terminationshok
terminationshok

Answer 9 months ago

You know what? You can have two thermostats on this kind of heater. If you hook them up in parallel, either one can turn on the heater. That way, you can have the Nest set to whatever temp, and the the old mechanical thermostat that probably came with the heater set above freezing. If, for any reason, your power is out, or the Nest is unresponsive, the mechanical thermostat will trigger the heat if it gets cold enough.

As long as there is gas, the heater will work! These types of heaters just need a tiny voltage to work, and the voltage is generated by a thermocouple next to the pilot flame.

The only caveat is that if you set the mechanical thermostat high, you can't shut off the heat with the Nest. If any thermostat calls for heat, the heat is on. Just set it low, and put it somewhere that nobody will mess with it. It can be an important failsafe.

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COBRAGUY42
COBRAGUY42

Reply 9 months ago

NO FREAKING WAY!!! I never even thought about that. Just tuck it away somewhere... I'm totally going to do that. Thx!

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msenn77
msenn77

Answer 11 months ago

As I recall right after I installed this in my home I was having charging issues and it ended up being that the small gauge wires from the AC adapter weren't making good contact with the terminals in the base of the Nest. This was the reason for tinning the ends of the small wires. I'm struggling to come up with a reason why this would be happening as mines been running since without issue. Do you get an error message on the Nest?

0
COBRAGUY42
COBRAGUY42

Reply 11 months ago

Woah..... guess what I did?!?!?! Didn't make sure the adapter was 12V AC. Mine didn't say DC but had a line under it. I looked it up and it was DC! Just went grabbed a 24 AC transformer and bingo! Been barely hanging on with 12 VDC for 2 years... yikes.

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msenn77
msenn77

Reply 11 months ago

Whoa indeed! I'm surprised that worked at all. Weird.