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Wednesday, March 13, 2019

NEST thermostat for my Rinnai monitor heater

I heat my home in rural Maine with a combination of a DIY installed heat pump, propane and a large wood stove.  (Since installing the heat pump in March 2121 the propane is now used only as a backup).  I have 2 Rinnai monitor heaters - one in the living area and 1 in the guest bedroom.  The wood stove in the basement is capable of heating the whole house, but I only fire it up when the temperatures drop below 20F which is often in the winter.  This strikes a balance for me of cost and performance - and carbon footprint.  I cut and split about  20-30% of my firewood from my own property here in rural Maine

I have been exploring different ways of controlling the big propane heater in my living room.

It's a 20 year old model that has a manual switch that you push-on/push-off and a simple slider to set temperature.  

A while back I built an interface that allowed me to use a regular programmable wall thermostat to operate it by replacing the power switch with a relay, and that worked relatively well.  But my schedule is erratic and I wanted the option of remote control.  The NEST thermostat E is a very appealing thermostat, but I had considered it too expensive until I found a used one one on eBay for about $80.  (The newer E model lists for $169, and the previous one is $249 and these prices are way more than a regular programmable thermostat that sell for $45 to $65.)

Here's the hookup info for the relay I used to control my heater.
I used a 24VAC power adapter that I got on Amazon that is sold specifically for home thermostats. (As an Amazon Associate I earn from qualifying purchases.)

I also bought a 24VAC relay from Digi-Key (their part number: Z9722-ND ).  It was pretty simple to hook these items up with the 25ft. of wire that came with the adapter.  I did have to get inside the heater and install the relay in there, and it was not something I would recommend for anyone not experienced with wiring or electronics.


This setup works really well for me.  Here's what I like about the Nest in particular.  First, I can control the thermostat setting from anywhere using my phone.  The user interface is excellent and it is extremely easy to program a schedule.

I also like that I can review the history that shows hours of operation per day and the individual cycles.

And the main screen could not be simpler:

Since I have installed an Alexa echo dot, I can say: "Alexa, set the thermostat to 68" and she set's it instantly.  This is nice if I decide to get up earlier than the scheduled time because I can use the 2nd echo dot in my bedroom to turn the heat up before I go downstairs.  Or, similarly if I decide to knock off work early I can set it from my office using the app.

Another clever feature is that the Nest can be programmed to set the heat back if I leave home.  It uses the IFTTT app to geolocate my home and can tell when I leave the area.  Overall I could not be happier with the Nest and all its features.

In my next post I show how I built an external relay box to control a portable electric heater from the Nest E.

21 comments :

  1. Hi Gus, this sounds interesting as I have a similar heater. Question, I am guessing you don't really use the slider to adjust temperature, you just leave it on a setting that will turn on when the Nest demands heat. Is that correct? Thanks.

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  2. Yes, I leave the slider on the Rinnai at about 80F equivalent so it turns on full blast when heat is called for.

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  3. Where you able to find a mounting base for the relay noted in your description so that the relay is securely fastened? If yes, do you have a part number?

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  4. I found one on Amazon that comes with a socket, search on: OMRON INDUSTRIAL AUTOMATION MKS2PI AC24 Power Relays, MK-S Series, Power - General Purpose, Non Latching, DPDT, 24 VAC, 10 A

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  5. . . . but you can just solder onto the relay and then wrap it in tape and let it hang loose in the heater. That's what I did.

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  6. I also live in Maine and I also have the same exact model rinnai haha. I'm just looking to hook it up to a normal wall thermostat. I'm no electrician so any advice? How complicated is it to do so?

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    1. You definitely need electronic skills to do what I did. So try and find someone who understands what I did an they should be able to figure it out.

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    2. Likely already solved, but for others... maybe IFTT would work with the Nest to turn on / off a heater via a smart plug?

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    3. Great idea! Although I have found IFTTT to be unreliable at times.

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  7. Are you relaying the power supply, just switching the power on/off, or are you relaying the switch allowing the unit to appropriately cool down before turning off?

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    1. The relay contacts are in parallel with the power switch, so this does allow the heater to cool down after the switch/relay is opened. This is been working perfectly for a year now!

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  8. I'm in Maine too and I'm trying to figure out how to keep the house 40 while i'm gone. I have an oil boiler & just got the Nest E. All that works. However, the power goes out sometimes. I don't want to install a generator.

    So I thought I can have a computer UPS with a heater like yours plugged into an Amazon smart plug. So I could leave the unit with toggle switch set to on, but smart plug off. When power goes out, I'll notice temperature dropping. Then I turn smart plug on to start the gas heater. I'll leave the gas heater in the basement clear from everything. If it doesn't start, I can cycle the power with the smart plug.

    Curious.. how many watts does your heater draw? Any suggestions for heaters? Thank you! -Matt

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    2. I didn't measure the wattage of my Rinnai propane heater. But it's probably less than 200 Watts. A UPS wouldn't have enough power to run it for more than an hour or so. But you should consider researching an Eco-flow unit that can be charged from solar or AC. They're pricey, but worth it. Even one of their small units would run a few hundred watts for many hours.

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    3. Hi Guy. In Waldoboro here. So the heater you have a photo of here is a Rinnai? I should have said that I don't need a fan.

      What I'd love to find is a heater that will switch itself on when electricity is applied and turn itself off when electricity is taken away.

      That's why I was intrigued by the photo of the heater you have on this page. It has that toggle button, which looks mechanical. I could leave it on, and the turn the heather on / off with a smart plug.

      This is going to be for remote operation.

      Or is this just a horrible idea (explosions... fire!)

      Thank you

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    4. The Rinnai is a closed combustion heater so it needs two blowers one to circulate fresh air past the flame and another to circulate interior air. By using a relay to simulate the switch I was able to allow the Rinnai to do its normal cool down. If you were simply to power a thing like this and then shut it off it might overheat and that could be bad. I can't suggest other heaters at this point because I don't have experience with them.

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    5. OK I've almost arrived at an understanding, but not quite. One more question, please.

      Are there settings of the switches (without your mods) of your Rinnai heater that you can set such that... when you plug it in, it turns on. And when you unplug it, it turns off?

      I've never used a Rinnai... and you are certainly technical, so you are the one to ask.

      Thank you from Waldoboro

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    6. My unit has a plug that is hidden behind the machine that would be hard for me to access right now. But keep in mind that this model is over 20 years old and they no longer make it. The newer models have electronic controls that do not allow you to turn the machine on by unplugging and plugging it back in again so that won't work for you. I'm pretty sure the same is true of my old model which is why I had to do this hack to control it.

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    7. OK. That makes sense. Yes I started to realize what I wanted it to do is likely a big safety hazard. I'll figure out some other solution. Everyone around here has a generator and I think that's just overkill.

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I welcome all thoughtful comments and feedback!