The GNU remotecontrol framework leverages already existing Information Technologies of a Data Network, Web Server with a complete Operating System, Database Server, Remote Monitoring Server, and Email Server. The cost to implement GNU remotecontrol is then reduced to the following ordered list:
It is highly recommended you choose external sensors for your IP enabled thermostat having pre-wired cabling long enough to reach where you need the external sensor to reside. Adding in more cable between a device and an external sensor is often problematic. Mixing different cable types, in either quality of cable or type of cable.....or both.....very often result with problems to having accurate sensor readings. This pre-wired cabling, per manufacturer design and intent of their sensor, decreases the likelihood of the sensor resulting with skewed metrics. Most external sensors are extremely touchy. This is a good thing, as it provides you with accurate metrics. However, proper cable selection of an external sensor is paramount to proper metrics. Go with the option of a manufacturer having enough cable as-built to meet your needs and not splicing on additional cable.
Finally, consider the benefit of connecting your external sensor directly to your IP enabled thermostat, provided the IP enabled thermostat can accept it. The benefit of sensor averaging is highly valuable to improving system performance. A direct connection to the IP enabled thermostat also eliminates the need for another power supply to operate the external sensor.
The cost to implement GNU remotecontrol, in comparison with a lesser Energy Management strategy for any HVAC system, justifies the completion of a Cost Benefit Analysis to determine if GNU remotecontrol is appropriate for your circumstances. Most likely, it is.