Help making a heating pad

Hi folks,
Essentially, I'm trying to make a heating pad and I'm becoming terrible confused. . .

Let me start by offering some background on my project.

I'm building a fermentation cabinet that will be cooled by a window A/C unit. The cabinet will be split into two halves. The first half, with the A/C unit, will be for lagering beer and cold conditioning. Temps will be around 40° F. The beer fermenting in the second half show be kept at about 60°-70° F. 

The 120mm PC fan will turn on and blow cold air into the second chamber when the temperature drops below a set point.

I would like to have heating belts wrapped around the containers in the second chamber to bring the heat of the liquid up when it drops too low.

This is where I'm getting very confused. I'm basically an idiot when it comes to electrical work. . .

I would like to use about 7' of 30 AWG Teflon coated copper wire as my heating element.

I've calculated the resistance of the wire at .722 ohms (this is the part where you ought to start speaking up and correcting me).

Can anyone help me figure out what type of resistor I would need to drop the voltage down enough to get a 20W heating element? I'm starting with 120V from the wall.

The sketch below is the cabinet design.


Picture of Help making a heating pad
Flexwatt heat tape would prob. work great for this.
lemonie6 years ago
Copper is bad for heating things - resistance is too low. At 0.722 Ohms you'd need to run >27 Amp through it to get 20W.
You could use thinner wire, or use a beer-heating belt/mat designed for the purpose.