Review of the 3M Filtrete Wifi thermostat CT-50

I bought this today from Home Depot for $99. Installation was easy, but in order for the Wifi to work you need to supply a 24 VAC Common to the "C" terminal of the thermostat. Even though my house was built fairly recently, the HVAC installers didn't bother to connect the 5th wire (Blue one) in the thermostat harness to the "C" terminal of my furnace. The Blue wire was left disconnected, so I connected it to the "C" terminal of the furnace and then to the thermostat and I had the 24VAC I needed to power the Wifi card. If your furnace doesn't have the "C" terminal you can use a 24VAC transformer.

Installation of the thermostat was fairly straightforward but I don't like that the thermostat doesn't split in half like my Honeywell one did. It made installation a PITA. Also, the batteries are kind of awkward to install. A little bit of thought by the designers would have made this easier.

I had a hard time connecting to the thermostat over the Ad-Hoc wireless network it creates. I tried two different Windows XP laptops and neither one would connect. Fortunately, my desktop PC has a Linksys PCI Wireles card and I was able to connect to it that way in order to do the initial configuration and attach it to my WPA secured wireless network. I've read that it will not work with WEP which seems strange. From what I've seen the iPhone is the best tool for the job. My HTC Incredible didn't recognize the thermostat's Ad-Hoc network so it wasn't suitable for the initial configuration. Of note, is that the thermostat will reset itself after about 10 minutes and the 5 digit code will change. You'll need to enter this pin when attaching it to your home's wireless network.

One down fall is that there is no direct access to the unit VIA web interface to program it. Everything is done on the radiothermostat.com website. This works fine, but if you're Internet is down you won't be able to change any of the settings through Wifi. Judging by the times that the thermostat checks in with the cloud it seems as though the cycle is every 5 minutes. So, any changes you make shouldn't take longer than 5 minutes to take effect.

That being said the radio thermostat company is very "home brew" friendly and has released the API's for the controller to the public. This means that using simple HTTP GET and POST requests you can re-program the thermostat and query its settings. For instance, to set the target temperature of the thermostat to 68 degrees Fahrenheit and put it into HEAT mode using the cURL command line tool you would use (Thermostat IP address is 10.0.0.6):

curl.exe -d {\"tmode\":1,\"t_heat\":68} http://10.0.0.6

There are a ton of other API's you can access, here is a link to the API PDF document. API Document V1_0R3. This document is uodated often so the link might die. I have this copy shadowed here.

Changes you make directly to the thermostat using the API's take effect immediately unlike the cloud changes. You also do not need to authenticate when connecting to the thermostat.

There is an Android control app which is pretty cool. You can set the thermostat to Away mode, and adjust the temperature, as well as, view the current temp. There are also a couple of other features I probably won't use very often Being able to tweak the schedule with the Android app would be nice.

Overall, this is a really nifty gadget and should help on those days I leave the house and forget to turn the heat/AC down. It will probably take some time to pay for itself, but I love electronic toys.