I don't know if you are still awaiting replies to this post from April.
Maybe you've already tried your idea and either melted the relay, or not.

Having just messed up badly with something like this myself, I urge you to be VERY CONSERVATIVE with how much current you switch with an electromagnetic relay.

Also, use an ohmmeter to measure the off-resistance of the heater you wish to switch. I don't know about heater coils, but incandescent bulbs have very low off resistance -- leading to very high turn-on currents -- that need to be taken into account when controlling them with relays.

Another approach is to control a solid state relay (of more than sufficient capacity) with your micro-controlled relay. The downside is you then have to provide the power to that loop. These things are often quite cheap and durable.

Good luck!