Carboy heater from Adventures in Homebrewing.
About from AIH.. “The Carboy Heater is a small heating wrap that is stuck directly to the fermenter to increase heat by 5-20° F. This heat wrap distributes 32 watts of heat over an area of 2 square feet for a very gentle heat. Use electrical tape (recommended) to adhere to your carboy, plastic fermenter, or even your conical! For ultimate control of your fermentation temperature, use in conjunction with a stopper thermowell and digital thermostat.”
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