Oh that's a good one. I had a coal stove that had an idle timer (mechanical clock) to keep the fire going when the thermostat wasn't calling for heat. It stopped working and the factory said they don't make them anymore, but I could special order a thirty party replacement for $250. I replaced it with an Arduino, a relay shield and a 20 line program for < $10. If I was more electrically inclined, I could have powered it from the stove's power. Instead, there is a USB cord sticking out the back =]