I’ve been diving into the world of smart thermostats lately, and I wanted to share a project that turned out to be pretty handy. My workshop/garage is heated with a forced air overhead furnace that’s not very efficient, so it’s kept pretty low when not in use. In fact, it’s normally kept at just below freezing by using a “variable calibration” with an old-school mercury thermostat. One of the reasons I’d never installed a smart thermostat was that nothing went low enough—especially in my price range. So, here’s the alternative solution that allows basic automation of the furnace. The costs were minimal since all this was sitting on a shelf: an old thermostat from a previous renovation, a donor thermostat, a Sengled bulb I picked up for cheap, and a high-level trigger relay assembly left over from another project. The end result is a ZigBee controlled thermostat installed in parallel with the old re-calibrated thermostat that can either: - Be active and act as a high-temperature setpoint thermostat, or - Be inactive and the furnace is controlled by the old sub-zero calibrated thermostat. The process was straightforward and relatively quick to implement: 1. Pair the bulb to Hubitat and switch the driver to “Generic Zigbee Switch” to eliminate any on/off ramping. 2. Harvest the ZigBee module from the bulb. 3. Install the module and relay in the old thermostat using an old USB cable and some wires, secured with velcro. 4. Mount the thermostat in the shop/garage, wire it in parallel with the old unit, and plug it into a 5V USB adapter. No more walking into a cold shop and waiting for the heat or forgetting to turn off the heat! This worked so well that I even did another one for someone without a hub using a Wi-Fi relay. Would love to hear if anyone else has tried something similar or has tips for improving this setup! 