Filtrete 3m50 ThermostatAfter adding the Raspberry Pi Openzwave controlled lights, the Raspberry GPIO controlled garage door opener, and the EtherRain Sprinkler controller, I only had one more project on my home automation check list.

It was time to add a remote controlled HVAC thermostat.  I had reviewed many options over the last few months and ultimately I decided on the Filtrete 3m50 Wi-Fi Touch Screen Programmable Thermostat with Remote Access (wow that is a long name).

Why did I pick this one?

  • Cost – I paid around $100 for it.
  • Expandability – The Filtrete thermostat has “plug-in” radio modules called ‘USNAP’ modules.  The 3m50 comes with the Wifi version but you can also purchase Z-wave and ZigBee modules.  The controller actually has room for two USNAP modules but I have no clue what the benefit would be to the two radios.
  • Published Restful API – As a personal preference, I tend to support all things with open API’s even if the control software is great (which I think it is in this case).
  • Free Software – PC / iOS / Android apps that are all well tested and have positive reviews.

Why did I not go with Z-wave?

  • Lazy – All the software is ready to go.  REST API is easier to integrate with my existing Raspberry Pi served UI.
  • Cost
  • I can always do it later.

Common Wire / Powered Outlet Required Problem: Most of the new thermostats are power hungry.  If you are replacing an older thermostat that uses batteries or one of the old school mercury thermostats, you will have to hook up 24vac power to make the USNAP modules work.  This problem sounded like a big pain but there are several youtube videos outlining different solutions.  In my case, the common wire turned out to be tucked in the wall and just needed to be hooked up to the ‘C’ terminal on the furnace.  From my reading, the common wire is normally blue or black but might differ in your installation.

Other note: I am doing this in Texas where I think our a/c and heating systems are a little easier to deal with.  Please make sure to follow the directions for your setup and make sure to have the appropriate power turned off before starting the project.  (I also found in my reading that some people have 120v power running to their thermostat – so be careful.)

After figuring out the “C” wire problem, the rest of the physical install was a breeze.   The wireless part could be a little tricky for non-tech users.  The easiest solution is to create an account with the “Radio Thermostat” application on your iOS or Android device.  Once you login, the app will take care of connecting to the thermostat and run you through the firmware update and setup.

If you don’t want to do that,  with any wireless device, search for a new wireless network with ‘thermostat’ in the name.  You will connect to an ad-hoc network where the ip address of the 3m50 thermostat is  It will ask you for the 6 digit password displayed in the upper left of the controller.  From there you can select your wireless network and enter your wireless key and you should be all set to use any of the applications.

Cool resources:

API (PDF Warning)

Support Page – lots of info on common wire and setup.

Filtrete 3m50 Thermostat
Reviewed by Thomas Loughlin on November 20th.
I have had no problems with it after a few weeks of use. See installation notes.
Now that two weeks have past by and I have tried both the heating and cooling modes, I feel it is safe to say I like this product. The web interface is easy and the application for iOS and Android work beautifully. When controlling the thermostat remotely, there is about a 5 minute delay.

The biggest complaint I have seen involves connecting with the wireless network for the first time. If not using an iPad, the process is not very user friendly. If you have an iPad, create an account with the application and it will automatically connect to the thermostat and let you configure the new settings.

Rating: 5


  1. Hesam Askari -

    Cool stuff! Hey I have one of these thermostats and like to get started. Is it possible to buy the wifi module separately? Where can I buy it? Thanks!

    • Thomas -

      The model I have is a little dated but I believe you still can – and on ebay under “USNAP wireless module”. The z-wave and zigbee versions seem to be much cheaper.


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