NEST thermostat for my Rinnai monitor heater

I heat my home in rural Maine with a combination of propane and a large wood stove.  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.  In an ideal world I would replace the propane units with heat pumps, but that is beyond my budget for now.

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, and 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.