Controlling a heater using arduino.

I want to do an small project. I already have a thermocouple reading app and circuit ( everything works fine ), now i want to control a resistance heater with the thermocouple reading as input. After some T, the heater will be shot down. My first approach after a little bit of research is a transistor ( it is basic, but i do not want anything too complicate or expensive ). I do not want to measure temperature over 100 celsius degrees so it will work?, the transistor will be fine?.

Here is the idea:

Thermocouple reading -> Arduino->( after reach some Temperature from Analog 0, send signal to Output 0)->transistor receives signal->communication between current and heater resistance is off

depending on how the heater must be switched on (and which voltage it uses) one should use a relay (with a diode for protection). The relay can indeed be controlled by a transistor.

Before selection a solution one must first know or find out the voltage (and if AC or DC) and current demand of the heating element.

You could try to hack a line voltage thermostat, or maybe use something like this... http://www.morelectricheating.com/default.aspx?page=item+detail&itemcode=AUBE10048

If you really want to switch line voltage yourself, think about using a triac and do proportional control.