Hi Hufza,
What is the "Time constant" of what you are heating? How often will the relays be turned on and off??
You might want to use optically isolated Solid State Relays like this:
http://goo.gl/qnW6k
Another advantage: These relays switch at the zero-crossing of the AC waveform and so have less spikes and EMI..
DISCLAIMER: Mentioned stuff from my own shop...