UPDATED: How to use a smart thermostat with electric baseboards or wall heaters

Smart thermostat with wall heater
Technically it is possible to use a smart thermostat such as the Nest with electric baseboard or wall heaters, but we no longer recommend it.

Update Oct. 24, 2016

After further research and discussion with Honeywell, we’re revising our stance on smart thermostats.

We no longer recommend that you attempt to install a smart thermostat to use with our products.

In the past few weeks we’ve been in discussions with Honeywell to get more solidified recommendations on specific relays and thermostats that can be made to work with line voltage heaters. We even began the process of bringing new parts and products into our system so we could sell the solution directly.

Somewhere along the way we learned that the relays Honeywell was recommending for this install don’t actually provide enough power to support smart and wifi thermostats for the long term. Even though we have performed successful testing with the Lyric and Nest thermostats in our engineering lab, we have concerns about the ongoing reliability and durability of this work around. We suspect running a smart thermostat with one of these relays as the power source may lead to the draining of the thermostat’s internal batteries.

We’re attempting to get more information from Honeywell and will post any updates as soon as we have concrete information.

We’re truly sorry for those of you who found this post in the past. Our goal with our blog is to support our customers’ needs and to provide good, useful information to make them successful using our products in their home. We felt there were a growing number of you who were interested in having a smart thermostat or wifi control option with our heaters. In the past we felt this was a good solution. Unfortunately we don’t anymore.

We want to make sure you have the latest information.

Thank you for understanding.

We’ve updated the original post (below) to be more in line with our current stance on smart thermostats:

Looking to hook up a smart thermostat to your wall or electric baseboard heater? It’s technically possible to make one work but you’ll need to do a lot of extra work and research. Here’s why:

The Honeywell Lyric, Nest and other smart thermostats are designed to work with central home heating systems. Those are controlled by low voltage thermostats, which use 24 volts. Electric baseboard and fan heaters work with line-voltage thermostats, which can be either 120 or 240 volts. If you hooked up a low-voltage thermostat directly to one of our heaters it would fry the thermostat. Not the best way to spend $250.

But that’s where relays and transformers come in. The transformer converts the line voltage power into low voltage power to provide energy to the relay and the thermostat. The relay is then a bridge between the thermostat and the heater, allowing the low voltage thermostat to control the line voltage heater. (Keep in mind that you’ll need one smart thermostat for each older thermostat you are replacing.)

You’ll want to make sure that you have a relay that’s properly sized to provide power to your heater. You’ll also need to get a transformer that’s properly sized to power your relay and thermostat. (This is where you’ll need to consult your thermostat, relay and transformer manufacturers.)

You also need to check and make sure your transformer and relay works with your heater’s voltage.

Installation outline

The specifics of the installation process will depend on what thermostat, relay, transformer and heater you have in your home, but here’s how it will work in general:

  • The relay and transformer will need to be installed somewhere out of the way that is still accessible (like inside a closet, in a crawlspace or in an attic).
  • Line voltage wires will run from your circuit to the relay/transformer.
  • Line voltage wires will then go from the relay to the heater; all line voltage connections with the relay must be made inside a surface mounted metal junction box.
  • Low voltage wires will be connected to the relay/transformer (outside of the junction box with the line voltage connections) and will run through the wall to the thermostat, which will be installed on the wall. The relay turns the heater on or off using the signal from the thermostat.

Which smart thermostats will work?

We’ve tested this setup in our lab with the Honeywell Lyric and Nest but we can’t verify this method will work with all low voltage thermostats or in all situations. We also suspect that this installation method may drain the thermostat’s batteries, making it necessary to replace them on a pretty regular basis.

If you have to have smart features or Wi-Fi connected thermostats, this method will potentially work for you but we hope to have a better solution in the near future.

Paul Suarez

Paul Suarez

Paul is a highly caffeinated, uber organized family man that keeps himself busy finding and sharing the stories that make Cadet a great company. When he isn't writing, or shooting photos and videos, you'll likely find him searching for killer deals on Craigslist, playing classic Nintendo games or quoting his favorite movies and TV shows.

View all posts
  • Akash

    Hi Paul, thanks for the post. Is Cadet going to recommend/ launch any line voltage wifi enabled thermostats which don’t require relays? That will make it much easier.

  • Robert Shilling

    We have Cadet thermostats right now and the main one is hot to touch and reads the temp wrong. Trying to figure out our options for upgrading our heating system.

    I have 4 separate thermostats controlling areas in my condo. 3 for individual baseboard heaters in the bedrooms and the main one controlling the living/kitchen/diningroom areas with three baseboard heaters throughout those rooms. Is there a system that is home kit enabled or will link them up and allow me to control it via my phone?

  • Aaron Miller

    I connected a nest thermostat up to my 240 volt electric baseboard heaters and it exploded and caught the wall on fire. I think I mixed up the red and white wires.

  • Dave

    Paul I have a 2 different thermostats I would like your opinion on. I am looking for a WIFI thermostat to attache to a wall heater. I want the WiFi as I am often gone and my old house is very poorly insulated. I want the flexibility to have it warm when I get home. I know, insulate is the best answer and in the plan just not budgeted currently. The 2 thermostats in question are NUHEAT AC0055 SIGNATURE WiFi Touchscreen Programmable Dual-Voltage Thermostat the second is ATMOZ2-240-WiFi. ATMOZ also makes ATMOZ1-240 WiFi. What are your thoughts on these thermostats? Do you recommend the 2 pole or 1 pole thermostat?

    • Paul Suarez

      I ran your question past our engineering department. We have not tested the ATMOZ thermostat yet. We recently reached out to NuHeat and they’re not recommending using their thermostats with electric heaters, they’re specifically designed for floor heating. I will reach out to you offline with a little more info.

    • Dave,

      Unfortunately we can’t recommend either one of those thermostats at this point.
      We haven’t had a chance to test the ATMOZ yet. Our engineering team has reached out to NuHeat about their thermostats, but they don’t recommend you use them with electric heaters of any kind.
      Sorry. I sent you a more detailed explanation in an e-mail.

      • Dave

        Thank you, I hope there will be a company step and bridge the gap

  • ND

    Wondering if this solution would still work with the ecobee3 since it doesn’t contain a battery and uses the C wire (I think).

    • Good question. We just can’t recommend it at this point. Most (if not all) smart thermostats will use a c-wire to power the thermostat. Part of the issue as we understand it is that not all relays will provide enough power to support the smart thermostat in all situations.

  • Deb Heck

    I just started looking into this, I’m getting a Nest for the A/C and would love a way to bring my 8 separate baseboard thermostats into the modern era. I really appreciate you having this post and it’s update available to shorten my research! Keep working on it, you’ll have customers ready and waiting when you have the solution.

  • SlavaC

    Thanks for the article, Paul. Was looking as well in automating my baseboard thermostat for some time.

    Need some help with an idea, do you know what is the internal operating voltage of a simple electronic line-voltage thermostats like TH401 (http://www.aubetech.com/products/produitsDetails.php?noProduit=167&noLangue=2) for example?
    How about hooking to it’s power and connect a wireless enabled controller (esp8266 for ex.) to the push buttons and simulate temp adjustment remotely.

    • Thanks for reaching out. Unfortunately, we can’t recommend that you modify a thermostat in any way. If you have any follow up questions, we also suggest that you reach out to Honeywell/Aube directly. The TH401 and other electronic thermostats we sell are their products.

  • I was about to buy a Nest to power my new Cadet 240v Register heaters before learning it isn’t very compatible with high-voltage heaters 🙁

    I hope there can be a solution in the future, even if it takes a little configuration—being able to set a temperature schedule for these would be a huge help!

    • You could always use a line voltage programmable thermostat to set the schedule, but yes, we’d like to have a solid recommendation for a wifi/smart thermostat option. Our engineering team is revisiting this subject. We’ll update the post as soon as we have a good option.

      • Jimmy

        Hi Peter, it has been 2 months since this post. Have your engineering team looked into a Nest – Aube relay combo solution? From reading on the Internet, it seems to work.

  • Karl Dieter Erdmann

    Cadet Com-Pak 1500W, 120V model CSC151, https://www.amazon.com/dp/B000HM7U1I/ref=psdc_516188_t1_B000LNKW2C

    Honeywell RTH6580WF & Honeywell RC840T-120 https://www.amazon.com/gp/product/B00D5YLY2G/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

    Please let me know if I’m missing something. Thanks for article.

    • Karl,
      We updated this posting today in light of new information we recently received. It appears that the relay you selected doesn’t have enough power to run a smart thermostat. While it’s possible that this installation will work, we can’t recommend it anymore. We are truly sorry for the inconvenience. If you have any questions, please reach out to me directly.

      • Karl Dieter Erdmann

        @cadetheat:disqus , Thank you for the quick response. It seems some people use an external transformer/power supply? Has Cadet’s tested this approach to avoid draining the battery? https://www.youtube.com/watch?v=BgDseEF-4OY

        • We haven’t tried this approach yet. We’re researching all the options out there to see what we are comfortable recommending in the future. Be sure to check with your local codes to make sure you’re following the requirements.

      • Jason Lunasin

        Darn, This was something I was looking into doing…
        How much amperage does a typical Wifi/Smart thermostat require? (can’t find this anywhere for any product)
        Is it significantly higher than the rated 40mA of the 840T?

        • Jason,
          That’s one of the things that our engineering team has been looking into. We haven’t found that information either.

    • Hans Holm

      I have 3 nests controlling my 240v baseboards with 3 RC840T-240 and they work fine. Nest thermostats have batteries so as long as you hook up the wires correctly they will work fine. Unless the RC840T-120 has different specs than the RC840T-240 other than the obvious.

      • Jimmy

        I think the RC840T-120 does not have the transformer like the 240 and so you have to buy it separately to power the Nest.

  • mic shields

    hi paul
    i bought a 2 circuit 10kw relay (R841E1068) to connect two electric baseboard heating circuits to the relay to use one sensi wireless thermostat. i have most of the wiring figured out with two exceptions:

    1, i read on your cadet documentation that i should connect the white and white yellow together. i now have a combined white and a red wire that i need to hook up to the sensi. can you tell me which terminals on the thermostat i connect them to?

    2, neither the wiring diagram on the relay cover or the schematic in the enclosed docs show me how to hook up the wires from the relay to two separate 220 breakers. it only shows two wires (the blue connects to both loads and go to power. the black and black yellow go to the other power lead.) coming from the relay to power but i have 2-220 circuits coming from the panel running into the wiring enclosure. per the docs,
    the question is how do i wire the two wires from the relay to the four legs coming from the two 220 breakers?

    • Mic,
      I’m running your question through our tech support and engineering teams.

      In order to completely understand what you’re looking at, can you answer a few questions for us? What are the heater models you want to connect to this thermostat? What are the voltages and wattages of the heaters? Are they in the same room or area (no door between the heaters)?

      • mic shields

        thanks for any help sir

        • Mic,
          Our engineering team was requesting a little more info from you, I updated my response above with a few questions. I’m not sure if you saw it or not. If you can get back to me with the model heaters you’re planning on using (including what voltages and wattages they are) and if the heaters will be in the same room or area, we can better figure out how to help you. Thanks!

          • mic shields

            i have 2 heaters on one circuit totaling 3500 watts and 2 heaters on another circuit, also with 3500 watts. all are new marley 220V heaters, they are all in one large room. i used the formula of each cubic foot equalling 10 watts. i actually needed about 650 square feet 10 foot high covered so i decided on 7000 watts.

          • Mic,

            So although the R841E1068 is called a “2 circuit” relay, it can’t be hooked up to 2 breakers. Our engineering department says it’s actually means you can have 2 thermostats running off one breaker. I’m sorry for the confusion.

            I’m not seeing the reference to the “white yellow” wire on the Honeywell install guide myself. I’d suggest you reach out to our tech support team over the phone at 855.CADET.US or Honeywell tech support: https://yourhome.honeywell.com/en/contact-us

          • mic shields

            thanks anyway, paul.

            i am going to need to redesign from the wiring on up. if i cant hook up two 220 circuits to one relay, then there is no point in a 24 volt thermostat so no need for a relay as i need two thermostats regardless. might as well go with line voltage style. i will be returning the relay but thanks again for your help.

            by the way, the white and white/yellow stripe reference is only on the inside of the relay cover. check it out.


  • Hans Holm

    I bought three ecobee 3 thermostats and tried this.. Unfortunately ecobee3’s don’t have batteries like nest does so if the heat turned on and you attempted to adjust anything on the ecobee it would reboot. This exact thing happens with all three of my ecobee3’s.
    I used RC840T-240 relays but I tried another brand with the same results.
    Looks like I’m going to buy and try Nest. This time I’ll buy just one to test it before I go all in and get 3. 🙁
    Hopefully I save someone some time and money.

    • Jimmy

      Hi Hans, how does the Nest thermostat work with the Aube relay? I am going to buy them very soon.

      • Hans Holm

        I have three working without issue for the past couple of months.

        • Jimmy

          So does the RC840T-240 provide enough power to the Nest? In another word, if you remove the battery on the Nest, it still powers, right? There is no need to get another transformer for the Nest, right?

          • Hans Holm

            Yes, the power from the RC840T-240 actually charges the battery in the nest.
            I don’t think that you can remove the nest batteries.
            All you need is the RC840T-240 (if you have 240v heat)

          • Jimmy

            Thanks Hans, I will check to see if I have 240V or 120V. I remember when I installed the heater a few years back. I had the choice of 120V (2 wires) or 240V (3 wires) and I forgot what I picked but my house is wired for 240V. So if it happens that my heater is 120V then I will replace it with 240V heater because I do want to go to a modern thermostat like the Nest.

            (the RC840T-120 does not provide power to the thermostat like the 240).

  • ken nichols

    I am looking to install communicating line voltage relays into every baseboard heater (4) in main living space, and control with one thermostat that communicates with each relay. Do you know any combination of relays and tstat that work together?

    • Ken,
      Smart thermostats are still somewhat new to us. Let me ask our tech support and engineering departments if they’ve heard of anything like this. I will get back to you as soon as I can.

    • Ken,
      One more question. How many (if any) of these heaters are in the same room? In general, we recommend you have one thermostat per room. If you’re talking about wiring a few heaters in one room to one thermostat, that’s one thing. If you’re talking about managing multiple rooms with one thermostat, that’s another thing. Our engineering team is researching your question and we’ll have an update for you tomorrow!

      • ken nichols

        heaters are in adjoining rooms, e.g., Living room, entry, TV room, kitchen. No doors to block them. I am interested in common thermostat for all heaters.

        • Ken, Our engineering team is investigating a few more items on this. We expect we’ll have an answer for you tomorrow. Thanks for waiting.

  • RichardS


    2 questions on NEST controlling electric baseboard heaters:

    1- How do you configure the NEST for electric baseboard heater? They show options for heating system fuel source and include ELECTRIC. Is the ELECTRIC option the right one to choose? They say they don’t support electric baseboard heater.

    2- I have purchased a Honeywell 840T mechanical relay that supports “long cycle” times (e.g. 15 minutes). NEST does not specify a cycle time. Is the NEST compatible with this relay?

    Thank you very much! You are the only one helping with info on this subject. It is very much appreciated.

    • Hi Richard,
      Sorry I didn’t see this comment until now. I sent your question directly to our tech support and engineering teams to see what they can tell us.

  • Sophist81

    I have a 120v Cadet heater and would like to use a smart thermostat. Do you have a relay for 120v systems?

    • Hi Sophist81, I am looking for an answer to your question. We don’t offer any 120-volt relays ourselves. The one we have recommended in the past seems to have been discontinued.
      Let me check in with our engineering team and get back to you. Sorry for the delay.

    • So this relay from our partner Supply House will potentially work, depending on which thermostat you plan on using: http://www.supplyhouse.com/White-Rodgers-24A05A-1-Electric-Heat-Relay-120VAC-14416000-p

      I’d suggest you get in touch with Supply House and see if they can help you find the right relay for your heater and thermostat. They’ll have much more product knowledge about products that we don’t carry.

      I hope that helps!

      • Sophist81

        Thanks Paul! I am trying to use Nest and went ahead and ordered a product on Amazon that handles 120v and was recommended as a common purchase with the Nest. Hope that works… Will update…

        • Best of luck. I’d love to hear how it works if you don’t mind sending me an e-mail after it’s up and running: psuarez@cadetheat.com. Thanks!

  • Mayur Bhatia

    Hi Paul,

    I have a medium sized living room where I’m trying to add an electric wall heater. I will need something that is close to 3000-4000W. Is it possible to install a NLW452TW and use it with a Nest?


    • Mayur,

      Sorry I didn’t get back sooner. Just ran your question past our tech support person. You can use the NLW with a Nest if you connect the heater to a relay. Just remember that the thermostat built into the NLW needs to be turned up fully clockwise (don’t adjust it) and the fan/auto switch must be left in the Auto position for the Nest to control the heater. Built in controls should not be removed off the NLW or the warranty would become void.

      If you have any more questions, please let us know so we can help!

  • Victor Heresmann

    hi paul, im trying to get a system going a bit against the grain here in south america, can you go over my ingredients list? i want to daisychain or whatever its called, probably 3 baseboard heaters and control them with one wifi thermostat, looks like i will be needing a relay, but apart from that, are there any other ingredients needed?

  • Mark

    Hi Paul, the link to the relay on HD says that it switches up to a 5000W load. If I’m adding an EBHN1500W, I need a different/bigger relay to handle that load, don’t I?

    • Hey Mark,
      So what is the total load that will be controlled by the thermostat? 1500 watts by itself should be fine, but it depends on what else is connected to that circuit.

      • Mark

        There are 4 baseboard heaters I’m looking to replace… a 2500w in the living/dining room, a 1500w and a 750w in the master bedroom (angled walls/windows) and a 750w in the 2nd bedroom/sewing room. There are also 4 circuit breakers marked “heat”: 2x20amp that are joined together and 2x15amp that are separate. They’re old (80s vintage) baseboards, and old/simple thermostats in each room. I’m looking to replace the heaters with Cadet hydronics and the thermostats with a Nest/Lyric/Ecobee

        • Mark,
          So sorry we missed this over the weekend. I just spoke with one of our tech support guys. He said he’d love to help you with your specific installation directly. His name is Thomas and his e-mail is tjones@cadetheat.com.

          • Mark

            Thanks, Paul!

  • Thanks for the post, Paul, I’ve been wondering about this as I use a Nest v2 with my HVAC but have a Cadet 240v thermostat unit in a bathroom that doesn’t have any duct vents… and I was about to try and figure out which Honeywell relay might get the job done, but the HD solution is great!

    Any short guidance on the install since this unit has the built-in knob thermostat… or should I go through tech support?

    • Hey Jeff,

      I’m glad you found this post useful. Thomas from Tech Support suggested the post because he’s been getting calls on a pretty regular basis asking about this. He said he’d be happy to walk you though the process. If you want to give him a call, his direct line is 360-567-1325 or send him an e-mail tjones@cadetheat.com

      I do know, if you have a Com-Pak heater in your bathroom, you can remove that built-in thermostat pretty easily. Here’s a video that will show you how to do that:


    • For the NLW and SL models, we leave all of the original thermostats and controls in-place, turn them up and then label as shown in this photo.

Subscribe to the blog: