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The fans do consume about 3W of energy. But I can't really count that cost when I notice a temperature difference, in a generally big living room, of 2 degrees Celsius, while a general air conditioner would require several hours and plenty of kWh to do the same heating the fans extract from the fireplace's lost energy.
Fan Assembly for Fireplaces...View Instructable »
PCB Concepts and Materials
Circuit Board Design Class