Hack Your Nest Thermostat to Run a Gas Stove or Fireplace

If you, like me, heat your home exclusively with a gas fireplace or a free-standing gas stove, and you would like to control your system using a Nest thermostat, then this is the Instructable for you!

The only reason that the nest thermostat wont work on these types of systems is that they do not run enough voltage though their thermostat wires to power the Nest. So the trick is to power it another way.

First off, if you have an air conditioning system, then the Nest should be able to draw the power it wants from that and you should be good to go. If you do not, then you must trick the Nest into thinking that you do.

Just connect the thermostat wires as shown above and connect a 24 AC transformer (see next step) to provide the power. The positive lead from the transformer should go to the Rc terminal and the negative should go to the C terminal. In this way, you can trick the Nest into powering itself off of a transformer without putting any unwanted voltage over your thermostat wires.

These types of transformers are commonly available as sprinkler system components at your local hardware store.

I have been using this setup to reliably control my gas stove for over a year now with no issues, but of course, neither I nor Instructables can warranty your Nest or your stove, so hack at your own risk.

Happy Heating!

Step 1: 24 V AC Transformer

These are commonly available at your hardware store, usually in the sprinkler systems section and will provide the right voltage for your Nest.

I hid mine in the closet behind the wall where the thermostat lives and ran the wires through the wall for a clean setup.

Comments

[mojo_4664]

Works on the ecobee3 as well

[seanism1]

With or without a relay?

[joeshilling]

How did you do this with the ecobee?

[GeorgeM382]

FYI, it is likely that you do not need a 24V AC power supply. That is because the power end of the digital thermostat has to convert AC to DC anyway to function. And the power end doesn't care if it's AC or DC that is coming in as long as it is the right voltage, and - is hooked to C. I just used a 24V DC supply and it works fine. And 24V DC power supplies are common and relatively inexpensive!

[keepurpaddlewet]

After connecting the Nest Thermostat and 24V power, does a milliwatt wired gas fireplace still work if the power goes out?

[fasteddieriverside]

The answer is yes, if you have the correct setup. The key is keep the current millivolt thermostat hooked up at the fail-safe temp, so if the power goes out, your pipes wont freeze. The second is using a 2-wire thermostat kit that includes a relay (Amazon search for Venstar 2 wire 24 volt). I tested it out before cutting holes in the wall, making sure the Nest was powered, and running my furnace, then cutting its power and ensuring the old thermostat kicked in.

[JerryJ71]

Has anyone tried this on a relay triggering a 240v baseboard heater? I am replacing the old 2 wire 24v mercury switch thermostat. And would love to set up to a nest. I have seen a lot of warnings about baseboard heaters, but I assume if it already is using a low voltage triggered relay on the 240v baseboard heaters, this solution of adding an other transformed to provide common power like this should work. Any advise welcomed.

[twoLsRbetterthan1]

According to the Nest FAQ: "The Nest Learning Thermostat works with 95% of 24V heating and cooling systems, including gas, electric, forced air, heat pump, radiant, oil, hot water, solar, and geothermal." So, since you are replacing an existing 24V thermostat, I expect that it should just work. I would put a multimeter on the thermostat wires and see what the voltage is just to be sure.

[wkrueger]

I followed the steps and it works! The only weird thing is how much noise the relay makes... I can hear it all over my house. Any recommendations?

[cameade]

Works on an Emerson Sensi T-55 too. There's a jumper on the back of the thermostat body that connects Rh with Rc. You want to clip that to electrically isolate the heating circuit from the 24 vac that runs the thermostat. Hook up Rc and C to a 24 volt power supply. You'll be running a new wire from the nearest outlet to the thermostat. Hook up Rh and W to your millivolt appliance. In my case it was a gas stove with simulated logs. You DO NOT WANT 24vac going to the gas valve of your appliance. I confirmed there was no voltage on the Rh/W circuit from the power supply. It simply closes when heat is called to complete the circuit in your appliance. Sensi doesn't specifically address running a millivolt system on their website but they do mention that jumper and how it will isolate the Rh/W circuit for "multiple transformer" systems.

[pdillon007]

I did this as well with a third generation nest and got voltage on the control wires. when I read another Hack they said I would need a 24 volt relay that when current is applied it is closed. Where would I get the relay and what type or model do I need to purchase? And yes, I hooked up the wires exactly like your diagram. Can you help please?

[bfeucht]

This worked great for me. I pulled out the multimeter and confirmed no voltage is applied to W1 and RH when in this configuration. Shipping back the relay I ordered just in case I saw 24v.

[waldolc]

This is a really sweet hack. Now you just need to use IFTTT to automate your hack.

[read more]

I have bought it and do follow above. But cant see step 2 :(

[godfish]

What if I told you Rc was intended to power the Thermostat? and Rh was to power the heating equipment? Thermostats have been designed this way from the first home systems.