First off, they looked into a plug-in thermostat controller, and found a cheap one called the HeaterMate. Unfortunately it left a lot to be desired.

An Arduino with 40 lines of code, a temperature resistor, and servo are all that’s truly needed to save some dough with this thermostat by [Peter Hamilton].

Four engineers from Spark have pooled their skills and resources to create a new open source smart thermostat based on Arduino using $70 of components.