I support the former suggestion of using a zero crossing relay e.g. Croydom. In selecting one such look out! many have been burned on not reading the specs and not taking into consideration that the resistance of the heating element can be much lower when cold. Another factor is spikes on the supply, some relays are specified at RMS, some at max which require you to divide by root 2. Use a relay rated much higher than you (think you) need and you will live happily ever after,

Erik