My electric furnace runs on 220VAC at up to 15 amps. The controller presented here precisely sets the average power by turning a knob. I designed and built this controller back in 2007 before I was comfortable with using Arduinos. I now know that it would not take much to modify the design to both have input from a temperature probe and be under software control. These upgrades would be particularly useful during the long power-up phase.
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