From the product description, check product page for current description, price and availability:

Keep your yeast happy and your ferment warm during those cold winter months with this flexible heater wrap! Unlike those old heater belts, the FermWrap covers a wide area of your carboy or fermentation vessel, promoting an even heat distribution (11″ tall x 25″ wide.). Using tape to adhere, the FermWrap can be attached directly to your fermenter, or can be used to heat the space in a box (or refrigerator) that the fermenter is in. Depending on your configuration and insulation, you can increase the temperature of your ferment from 5-20 degrees Fahrenheit. This differential can be increased by using our carboy bag to insulate a carboy (this has been tested). To decrease the temperature differential, stick only a portion of the FermWrap to the fermenter.

With 40 watts of heat spread over almost two square feet it provides gentle even heating. Draws 40 watts. 115V.

For more precise results, we recommend a temp controller and carboy thermowell for the ultimate in fermentation temperature control. Or for the best control, use the dual stage control and carboy thermowell, as well as a refrigerator, to control both the high and low temps.