I am a HVAC service technician, and personally I believe selling these thermostats or any thermostat to the general public is a bad idea. I couldn't tell you the amount of calls I have ran where someone has purchased a new thermostat, attempted to install it themselves, and fried other components in their system during the process. I've installed a few of these, and they are nice. My advice to anyone who is getting one is to make absolutely sure it is compatible with your current system first. Second, if your not 100% sure how to install one without any problems, call a qualified technician. Those letters that the thermostat wire hooks up to (R,Y,G,O,B,C,W...) don't represent colors. Although the voltage in those wires is only 24v, that is what your entire systems control voltage is, and the cost of repairs to a improperly installed thermostat can be extremely expensive.