Xtension now supports ZWave, direct serial or networked connections to several brands of communicating thermostats. Replacing a thermostat should be within the skills of any home automation enthusiast keeping a couple of things in mind.
If you have a Vera interface for Z-Wave then any Z-Wave thermostat that is compatible with it will also be supported by XTension. This is the preferred way to connect a thermostat to XTension. If you wish to use a non-zwave or directly wired thermostat XTension supports several different kinds natively. Please note that ZWave thermostats may not function with the older legacy Z-Wave interfaces that are in legacy support.
The Omnistats and Aprilaire thermostats require getting extra wires to the thermostat location for communication. This can be difficult or impossible in some cases though they are both excellent devices. If it is not possible to get a wire to the thermostat then consider the RCS model. In that case it is only necessary to run a cat5 or equivalent to the furnace itself where the control box is. The RCS also does not require a wifi or other network beyond it’s serial port connection. If it’s not possible to get a wire anywhere but you have wifi at the location then the wifi thermostat is a good choice.
I would also love to support the new “nest” thermostat but as of this writing there is no API for talking to it and no announced plans to release one. If and when this changes I will add it to the list.
You must turn off the power to your furnace before working with the thermostat. For a system with AC there will be the dual gang breaker for the compressor and a separate single gang one for the furnace. Normally the 24v transformer for the control boards and thermostats will be on the single one. Make sure the thermostat has gone dark before you start taking the wires off. This arrangement may be totally different on more complicated systems or systems with multiple zones or separate power supplies for vents and duct controls and such.
24v is not enough to give you a shock, however if you short the power to ground while you’re moving wires at the very best you’ll blow a fuse hidden somewhere inside your furnace and at worst you’ll burn out the 24v transformer necessitating a service call and being without heat or ac until they can get out and replace it for you leaving you to pay for a service call and a new transformer. Additionally letting the power come into contact with the other leads may put a great deal of strain on your compressors and other components which are usually protected from immediate restarts or stuttering by the thermostat logic. Just find the breaker and turn off the power.
Take some pictures or take notes of the connections of wire colors and terminal labels. These things are not standardized and if you use non-standard wires or change things make a note on a sticker inside the stat to remind you later. Here I extended the wire with some sprinkler wire because that was all I had and it has a totally different color scheme. Inside my thermostat is a brother p-touch label with all the info on it so I cannot ever forget.
These stats have dip switches to setup the kind of stat they are, gas/electric/heatpump etc. These must be set right for your system or it will not function.
If things don’t line up obviously with the new stat you may need help. Especially with more complex multi-staged systems or systems with vents and remote sensors replacing a stat can be much more complicated due to the lack of standardizing of what goes where, what it’s called and what color it is. Better to pay for a service call for a thermostat install than for expensive internal bits of your furnace system.