Wrap around brew heater.
Suitable for various sized fermenters, glass or plastic.
Heat belts are more flexible in their use than heat pads as you can control their heat output by their location on the fermenter. Placed lower down they will provide more heat than when placed higher up. (see attached picture for a demostration of a heat belt in use)
Turn the appliance on when the brew is dropping below your desired temperature range and turn it off or move up higher if heat is getting too much.