Google nest hookup for a millivolt gas heater

[Novice]

I have a 2-wire millivolt gas heater. It seems I need to connect the two wires from the gas valve to W1 and RH and then use a 24V transformer and connect them to C and RC on the more expensive google nest. The basic google nest has G, R and OB on the right side and Y, C and W on the other side. How do I translate W1, RH, C, RC to the basic google nest terminal labels?

[dhx227]

I'm pretty sure the Nest will not work with a millivolt system without the use of an external 24VAC-based relay.   The Nest is not like a thermostat that typically uses internal relays to switch on/off the call for heat/cooling and thus don't really care what the voltage being switched is.   The Nest is all solid state, so likely will not work to switch a millivolt relay.  What you could do is use something like a RIB U1C (https://www.amazon.com/Functional-Devices-RIB-U1C-Relay-Box/dp/B006YVL93Q/) to switch the millivolt side, then you supply the Nest with 24VAC and wire the RIB U1C as if it were the furnace. 

This would be your wiring guide:

• 24VAC transformer wire 1 - to (C)ommon on Nest and WHT/YEL on RIB-1UC.
• 24VAC transformer wire 2 - to Rh on Nest (Rc is for power to cooling circuit switch)
• Nest W1 to WHT/BLU on RIB-U1C
• Boiler wire 1 to YEL on RIB-U1C
• Boiler wire 2 to ORG on RIB-U1C

[Novice]

Thank you! The only issue is that basic google nest has terminals G,R, OB, Y, C and W as in the photo I attached. What would be the proper wiring for basic google nest?

[dhx227]

Per the wiring above, just use the R instead of Rh, and W instead of W1.

Only FYI, this is the meaning of each of those wires:

• C - common
• R - power source to use when calling for heat/cooling or switching heat pump operation
• W - call for heat
• Y  - call for cooling
• G - independently controls the fan only
• O/B - typically used to control the direction of a heat pump (heating or cooling mode)

Note: the thermostat will effectively connect R to any particular wire of the last four to enable that function.  Classic thermostats would do this through the use of internal relays.

I'll also add that the reason the other Nest has the more complicated wiring is because when you have independent heating and cooling units, they often each have their own transformer.  You can't intermix the power from one transformer to another (it simply doesn't work).   So, in those cases, you need a separate Rc (for the transformer used in the cooling system) versus an Rh (for the transformer used in the heating system).   The thermostat then needs to appropriately switch Rc with Y1 (and optionally the second stage Y2), and Rh with W1 (and optionally second stage W2).

[Novice]

Thank you so much! Please bear with me: Does this mean that I need 3 components:

• nest thermostat
• a 24V transformer
• RIB-1UC

Or does RIB-1UC also provide the 24V power that nest needs?

[dhx227]

Yes, you will minimally need those three components.  And no, the RIB-U1C is just a relay.

As for the transformer, I would recommend you get a UL-listed Class 2 or 3 transformer.   It doesn't need to be very strong transformer.  Transformer's are rated in VA and for this job you really only need one that is minimally rated 10VA.   But the smallest 24VAC transformers tend to be either 20VA or more commonly 40VA - that is fine, it's just way more than what you actually need to drive power for the Nest and operate the RIB relay.

[Novice · Accepted solution]

Thanks a lot for edcating me!

[muncle]

I want to wire my millivolt heating system using this method but I have HVAC controlled by nest as well. HVAC has R,G,W,Y but don't want to use its heating for a few reasons. So basically W is left disconnected. So can I omit the 24V transformer and use R from HVAC as power? Then wire relay to W and C?

[dhx227]

Yes, that would work (assuming you then also connect W at the Nest).

[Jhonleanmel]

Hey folks, 

We appreciate your help here, @tgadgets.
I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,
Mel

[tgadgets]

Nope. I'm good. Everything is functioning just fine for many months now.

[Jhonleanmel]

Hey there tgadgets, 

Awesome — glad to hear that your issue is fixed. It looks like we can consider this one complete, so I will lock the thread shortly unless I can help out with anything else. 

Best, 
Mel

[tgadgets]

I had the basic Nest and I used terminals R, W and C.

[tgadgets]

This worked perfectly. Thank you.

[goalie6966]

I only have the red and white wire from the boiler and the 2 wires from the 24v transformer, how does that get wired to the Google nest smart thermostat, do I add a wire from the relay???

[Novice]

---

@Novice wrote:

I have a 2-wire millivolt gas heater. It seems I need to connect the two wires from the gas valve to W1 and RH and then use a 24V transformer and connect them to C and RC on the more expensive google nest. The basic google nest has G, R and OB on the right side and Y, C and W on the other side. How do I translate W1, RH, C, RC to the basic google nest terminal labels?

---

Thank you! The only issue is that basic google nest has terminals G,R, OB, Y, C and W as in the photo I attached. What would be the proper wiring for basic google nest?

[tgadgets]

I have what you have and I used R, W and C but in the drawing above they do not have the relay in there like  

dhx227 told you that you needed. I used another drawing to help me with what dhx227 was saying...

 

[dhx227]

Nice!   And thanks for finding the perfect picture to complement my instructions!

[tgadgets]

dhx227 really thank you for the instructions. I have wanted to put my gas stove on a Nest for quite a while and Nest just kept telling me it was not possible. I bought the relay that you had a link to above and a 120v to 24VAC tranformer. I had a light switch in the wall below my thermosat so I pulled out the box and put in a three gang two of which were for switches... the third I filled with transformer, wiring and screwed the relay on the outside of the box (but in the wall) with wires coming into the box from rear. I put a blank in the third opening for a switch for the cover and everything turned out beautifully. Thermostat works like a charm and I can control it like my house thermostat with Google Home. Very happy with this setup. Thanks again for taking the time to type up the answer above.

[Novice]

I thank both of you (dhx227 and tgadgets)! I have not yet bought the components needed for this solution. tgadgets: Since you have already implemented the solution, will you please share with me the exact model of the nest, relay and transformer that you bought? As my name shows, I have to make sure that I don't make any mistakes along the way to this solution. Thank you all again!

[AVHVAC]

@tgadgetsI am also interested could you please share?!

thank you all for paving the way

[AVHVAC]

That or @Novice did you end up purchasing anything?

[Novice]

After getting all the details, my new dilemma is this: With the current milivolt thermostat, my gas heater will work even if there's a (long) power failure. With the modified nest thermostat, Gas heater will not kick in if my cabin loses power. Since I also lose water when there's a power failure, I have focused on getting a proper size UPS before I switch to Nest.

[AVHVAC]

Got it. After more research I might just get a programmable thermostat and wait till my next place before I get a switch

[tgadgets]

Transformer: https://www.amazon.com/gp/product/B086S79N1C/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

Relay: https://www.amazon.com/Functional-Devices-RIB-U1C-Relay-Box/dp/B006YVL93Q/

Nest Termostat: https://store.google.com/us/config/nest_thermostat?sku=prd_7577_5352&utm_source=sem_pla&utm_medium=d...

[Novice]

tgadgets thank you so much for the detailed list of components. Will you please confirm my assumption that once I switch to this system, it won't work unless there is power. The milivolt thermostat doesn't need power to work. In other words, I need a UPS for uninterrupted operation of my gas heater once I switch to (modified/enhanced) Nest thermostat.

[tgadgets]

Yes, you will need power. I co-located mine in a box with other light switches for the room. I had two light switches in one box for the room. I replaced the two-switch box with a three-switch box and put the transformer and relay there along with the previous two light switches. I had to mount the relay on the rear outside of the box, but it worked well.

[dhx227]

I'm curious, does your gas heater not have a blower fan to circulate the air or a water pump to circulate through radiators, or is this just something like a fireplace? FWIW, you would be amazed at how much more efficient heating is with even a simple oscillating fan to push the heated air around! But yes, this setup does require power, though very minimal. You would probably be fine for quite some time with even the smallest UPS you could buy. Apparently, the Nest uses "less than 1Kwh per month" (that's the best power consumption that Google can provide) - so let's translate that to 1000/30days/24hrs = 1.39 watts per hour (truly not very much). The relay will consume 1.1 watts while activated. We could also assume about a 5% power loss in the transformer so, let's just add one more watt for overhead. So, while actually heating, that's roughly using ~3.5 watts. So, depending on how long you want this to run on the UPS, you can then take that number and multiply it by time. Or let's say, you want it to be able to run for at least 24 hrs, then that would be just 84 VA. As an example, this small UPS on Amazon (https://www.amazon.com/CyberPower-ST425-Standby-Outlets-Compact/dp/B07GZR981Y) is rated for 425 VA and would likely last you at least 5 days! Note: this is also assuming worst case where the relay is ON for the entire time) - in reality you would probably get 7-10 days out of that 425 VA.
Note: those calculations are based on estimates from spec sheets; I have not actually measured consumption of these devices. However, they should be more than sufficient to estimate the ballpark usage and gauge what size UPS would more then suffice.

[Novice]

It looks like a wood burning stand- alone stove but burns propane and has a milivolt thermostat. It has no fan. I agree with your estimate of UPS power consumption. As I mentioned, I am thinking of getting a much larger UPS to supply power for the whole cabin for three days. It shouldn't be too large since the main power consumption is by the water pump in the well (which is crucial. No power, No water!).

[tgadgets]

BLUETTI AC200MAX Expandable Power Station | 2,200W 2,048Wh (bluettipower.com)

[dhx227]

If you have room on top of the "stove" you should consider something like this (if you don't already have one): bybule Heat Power Wood Stove Fan with Heat Protection Glove and Thermometer,Fireplace Fan for Wood/Log Burners/Fireplaces(6-Blade) https://a.co/d/fPswcci