The simplest is a Triac controller on the transformer secondary, the best usually is a toroidal type as they are easy to modify by adding or subtracting windings, but with the triac control it shouldn't be needed.
I would put the control after the secondary rather than on the primary that some do when using a off the shelf dimmer.
A triac controller is fairly simple to build and Google will show several examples.
Max.

 

Your question implies that you are connecting the 13 wires in series. While this certainly is possible electrically and physically, it moves your power requirement into an unpopular market segment. In other words, good luck finding a 160 V, 1200 W power supply.

OTOH if you connect the 13 wires in parallel, your power supply now is 12 V at 100 A. This is off the shelf at Digi-Key, Allied, Newark, Arrow.....
http://www.digikey.com/product-sear...1&stock=1&quantity=0&ptm=0&fid=0&pageSize=500

ak

 

Were the wattage figures calculated on the basis that the wires at a temperature of 700F are radiating into free air? If so, the figures may be a tad optimistic, since no allowance is made for the heat lost by melting the foam.

 

You are going to need regulation or control of some kind, this is easier to do at the AC level, you don't necessarily need the extra cost of DC supply, IMO.
Max.