This 30w Heating belt will gently warm without creating major hot spots on your fermenter. 
One reason to go belts over pads for the simplicity of adjusting the height of the belt on your fermenter to increase or decrease the heat transfer. With a pad, you're unable to do this, and may potentially cook your yeast turning your hard work into a giant bandaid.

We highly recommend using a belt with a temperature controller for precise temperature control. If you're fermenting in a fridge, you can also use the controller's cooling function as well to control both the belt and the fridge.

Element Length: 90cm

Please note these belts are not designed to be used with Fermzilla's or thin plastic fermenters as they can cause warping.
For Fermzilla heating see the heat wrap here

For thermostat control and to keep the belt at a cetain temperature you can hook this up to either of the below controllers.

STC-1000

Rapt temperature controller