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Update December 2017:

I've had several people email me asking if the ecobee 3 or ecobee 4 will work. The short answer is no, they will not completely function from a 12VDC source. They will sort of boot up but not work. The ecobee Si is the only ecobee thermostat that I'm aware of that will run okay from a 12VDC source voltage.

I'm fairly sure I tested a Honeywell 'smart' thermostat when starting this conversion project and as I recall, it ran fine from 12VDC. And no, I don't remember the model - sorry.

Having said all of that, it IS possible to make the ecobee 3 or ecobee 4 work if you are willing to assemble several relays to operate from 24VAC to switch 12VDC to the basement air and/or gas furnace but that is beyond the scope of my project.

If you manage to get something like that working, email me the details and I will publish your project assuming you want to share.

 

Why you might ask?

Over the past few years I have come to really dislike the Coleman-Mach thermostat for several reasons. A primary issue of mine is the decidedly user-unfriendly sliding mode switch, in my opinion this was a very poor design and engineering choice because it's very difficult to "feel" the switch detent for the desired mode (off, cool, heat, etc.) and the switch (actually two ganged switches) is most likely a failure focal point. Primary gripe number two is the fixed five degree delta before auxiliary heat (the propane furnace) is called when the heat pump coils freeze up. Five degrees doesn't work for everybody and certainly not me. And a last major issue for me is no automatic changeover from heat to cool, or vice versa. We spend usually 4-6 weeks in Colorado every summer and you need heat in the early mornings and air conditioning around mid-day. I got used to auto-changeover thermostats in our last two houses and have come to appreciate the set and forget beauty of this feature. Another nice feature is the Internet connectivity ability of the Ecobee thermostat which we will discuss elsewhere.

A few caveats before we get into the project

While I have many, many hours of research and trial and error into this project and while I'm very confident the new Ecobee Si Smart thermostat installation will meet or exceed my expectations, I'm considering this project in the Beta stage of testing for now. Once I have a month or two of out and about (on the road) experience with the Ecobee, I will update this write-up.

Update June 1, 2014

We now have enough experience with the Ecobee thermostat both on the road and while parked to consider it ready for prime time. It has completely met and even exceeded my expectations and has not exhibited any anomalies or bad habits. We have used it in a variety of weather conditions from too cold for the heat pump (it went into gas heat mode nicely) to cold at night and warm in the daytime requiring change-over from heat to A/C. In all scenarios, the unit has worked great.

The other point I would like to make about the Ecobee thermostat (I will sometimes refer to it as the Ecobee, Si or Smart Si) is that it's designed for a residential house and not an RV that's on the move. The primary impact of this concerns Internet connectivity (the Si has WiFi capability) - you will not be able to use the on-line features unless you reconfigure the Si every time you park for whatever WiFi that's available. Will the Si work without Internet? Yes it will and it will work fine but you won't be able to remotely access the thermostat or look at the weather forecast or have the thermostat display what it thinks is the outside temperature.

You assume all of the risk if you attempt to follow my directions/instructions and I don't offer or make any warranty or claim, implied or otherwise that the instructions and wiring are 100% accurate. Your mileage may vary, your results might be different, yada, yada, yada.

Before you do anything, study all of the instructions, my wiring chart and the various RVP and Ecobee manuals/guides and completely understand what's going on. Do not tear into the project armed only with my wiring chart! You have been warned!

So what all will this Smart thermostat do for me?

The feature set of the Ecobee Si is very rich and I'm not even going to attempt to describe it in my write up. Please go here for a tour and do some reading on Ecobee's web site. The Si user manual is here, and the installation manual is here.

Is this something I can do myself?

Skills required are familiarity with wiring (some electronic experience desirable), soldering, access to a 25 watt pencil soldering iron, heat shrink tubing, mechanical and general DIY abilities. Changing out a house thermostat is a fairly simple project for even those with moderate DIY skills, replacing the Coleman-Mach thermostat is more involved primarily because of all of the various wires involved and if you take my advice and solder solid thermostat wires to the stranded Coleman-Mach thermostat wiring. You will need to do your own research and verify and check my instructions.

Also please note - I am NOT going to walk you through every small step or detail of this project - if you need that kind of detail and hand holding, I recommend you find a geek or electronic tech and let them help (or you help them.)

Could something go wrong to where I've ruined either the heat pump, the original thermostat or the new Ecobee?

That could be a possibility, but in my opinion a remote possibility if you are careful. The very first thing to be aware of is that there is one red/white wire coming out of the three pin connector that will have +12 volts on it. Identify it and make sure it doesn't contact ground (or -12 volts) and short out.

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