Many stoves use millivolt jacks on their stoves. This poses a problem when you want to use a thermostat that had functions etc...especially things like Wifi. Basic heat only thermostats, such as mercury filled or the ye old slider style basically just complete a circuit when the temp falls below a specific set point. They don't need to be powered. As soon as you start using thermostats that have digital readouts, have clock, are programmable or connects to WiFi portals, one must power the thermostat. Most thermostats run on 24 volts. Your doorbell on your house may run on 24 volts too. Most central heating equipment will have some kind of transformer that powers the thermostat via the Rh and W wire connections. However,these connections will only power the thermostat when the unit is calling for heat, and that's what the C wire on the thermostat is for...to provide a common neutral wire for when the tstat is NOT calling for heat. Many pellet and has stoves utilize milli-volt powered tstat jacks. The reasoning is that room heaters such as these should not be used as primary heating systems and as such and controls for them such as tstats should NOT be located too far away from the unit. Milli-volt current will not travel to far away so that is why they are used. What we don't want to happen is to have the stov calling for heat too soon after the unit has gone in to shut down mode. We call it short cycling and it can mess up the logic in the control board of the stove. Not permentaly, but perhaps enough to force the owner to unplug the unit and restart the system. It the pictures below I have made a powered relay with a 24v transformer to allow a pellet stove with a milli-volt tstat jack to be used with a 24v C wire powered tstat. The one I am using is also WiFi enabled. I chose the Cheaper one from lowes Honeywell 7-Day Programmable Thermostat Item #: 171234 | Model #: RTH6580WF1001 The relay is a RIB UC12 and the transformer I got from Radio Shack. The wires coming out of the j box to the left are not being used. The orange and the yellow coming out of the bottom go to the stove, the red wire goes to the Rh on the tstat and there is one white wire for the C connection and one for the W connection. It works like a champ. Here are some benefits... You can turn the stove on and off from work for your kids, start the stove on the drive home from work and have the house warm when you get home. Monitor the stove in a rental unit or a time share vacation home. Good stuff!