The Brew Belt is approx 1" wide and 32" long that wraps around fermenter to increase heat by 5-20° F with 15W. Two different springs (1" or 4") connect the ends to hold onto 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.
The environment drives the final heat produced, it will need to be kept on longer in the winter than in the summer.