Phase angle power regulation
Phase angle power regulation is probably not the way to go. It does
produce some fairly nasty harmonics and your neighbours will be
pissed at what it does to their TV reception.
All is not lost, however.
You are not the only person faced with this problem which is why they
produce zero-switching TRIACs. These devices only switch off when
there is no voltage across them. That rules out phase angle
regulation, but enables you to build a controller that is on for a
number of cycles, and off for a number of cycles.
It would be useless as a light dimmer (because your eyes would see
the flicker), but is effective enough to control a heating element.
The basic circuitry involves producing a sawtooth waveform (with a 2
second period) and comparing against a reference voltage through a
high gain op amp circuit. The output is a square wave where the duty
cycle varies according to the reference voltage.
It isn't that hard to put together and won't produce nasty harmonics.
Depending on the size of you elements you will see you lights dim and
brighten as it switches, but that's all.
Contact me directly if you want further information.