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.

4 People Made This Project!

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108 Discussions

0
kbenti
kbenti

4 months ago

I don't see the need for the relay. I have a millivolt system, and I connected it to the Nest with a 24Vdc source like you mentioned. Done, the relay is assuming you have a high voltage system, but the name "millivolt" is self-explanatory, there is no high voltage.

0
kbenti
kbenti

Reply 4 months ago

In reviewing my response to your proposal, I realized that you need the relay for your fan. My system has no fan. The relay is to power the fan, which will need something substantial.

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redheelerdog
redheelerdog

1 year ago on Step 2

Anyone know if there is a solid state replacement option for the White Rodgers 90-370 184-916 relay? Where I have mine installed the relay switch is rather loud? Thanks

Fan Relay White-Rodgers rbm type 184.JPG
0
foreverloveiphone
foreverloveiphone

Reply 5 months ago

Hi,

I wired as your instructed with 90-370 and it is working great But i am tired of the clicking of the magnetic relay and would like to change to SSR relay. Please instruct me how to rewire to get it done.

Your help is much appreciated.

SSR 25A.jpg
0
msenn77
msenn77

Reply 5 months ago

You're correct: The coil/magnetic relay is pretty loud. Unfortunately, the SS relay you've pictured here won't work as the INPUT side requires DC current and the circuit from the power adapter and Nest will be AC. You'll need something like this: https://www.alliedelec.com/product/sensata-crydom/a2440/70130417/

Wiring would be very similar to what I've posted. The OUTPUT side will go to the fireplace and the INPUT to the power adapter and Nest.

0
redheelerdog
redheelerdog

Reply 1 year ago

So the SSR numbered inputs and outputs are the same as the White Rodgers?
For the SSR connect 2 and 4 to my gas stove, and 3 to W1, and 1 to B&W AC adapter ? (like diagram attached) Thanks for your help!

Nest Diagram.jpg
0
msenn77
msenn77

Reply 1 year ago

i'm sorry but i provided the wrong link. Try this instead for AC input. https://www.amazon.com/dp/B01MZ2B0LA/ i believe the thermostate/adapter would to go terminals 3/4 and the 1/2 terminals to the stove.

0
redheelerdog
redheelerdog

Reply 1 year ago

Sorry to be a PIA, does that relay need 80V minimum to switch? Will the 24V PS be enough for it to work. Thanks again.

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msenn77
msenn77

Reply 1 year ago

oh wow. it appears i am batting zero -- i have been struggling with the stomach flu the last couple of days. yes, it probably won't switch at 24v so you'd need to find a relay that works at the 24vac supplied by the adapter that powers the Nest. in hindsight, this may have been another reason why i went with the electromechanical relay.

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msenn77
msenn77

Reply 11 months ago

Yes, I believe this option would work just fine also.

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wheelerjb
wheelerjb

9 months ago

hey guys, this is some very good info and the solution to my problem, for the most part. in doing some more digging, I was wondering if the 1N185 Relay from Grainger could be connected to still allow for the battery operated t-state to work if the power goes out? see attached. If I understand the relay diagram right, it can switch two seperate legs.

tstat hook up with battery backup.jpg
0
bradycommbrady
bradycommbrady

10 months ago

I have a question. I have a switch that turns on the flame and then there’s another switch that turns on the fan. How do you incorporate that? And after a few minutes when the thermostat inside the fireplace gets warm enough it turns on the fan

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goo2
goo2

Question 11 months ago on Introduction

After about a year of this setup working perfectly the nest started to say it didn’t have enough power and battery was too low it even shut off the WiFi . any ideas as to why this would happen? Nest is sending me a new thermostat to see if that fixes it but also thought a dedicated common wire would help? Any ideas?

0
msenn77
msenn77

Answer 11 months ago

Is your 24VAC power supply still functioning properly? There is another question in this thread where the person had two power supplies and neither were good. She replaced and all was OK again.

0
goo2
goo2

Reply 11 months ago

I actually created a common wire by adding a wire off of the 2nd wire from the transformer that plugs into the 1st spit into the relay... I believe this is a neutral? now I have a constant 24v and don’t have to worry about stealing power from the fireplace or pulsing and what not. Similar to this

0
msenn77
msenn77

Reply 11 months ago

I don't believe it's necessary and should function fine with or without. The relay is the device that isolates the 24VAC from the fireplace millivolt and vice versa.