Why use phase control for heating elements? PWM, also known as burst control, should be used instead.
Why not power the heating elements from mains, rather than off a transformer? That would get rid of the need to switch an inductive load. If you want to use a lower voltage, for safety reasons, then how about a 12V electronic transformer, designed for halogen lamps, or using DC?
A freewheeling diode won't work, because it's AC. Use a snubber network, consisting of a resistor in series with a capacitor, to dampen the high voltage spike.
True AC motors are generally unsuitable for phase control, to vary the speed, other than the shaded pole type, used in small fans. Universal motors, which have brushes and are work off either AC, or DC, can be speed controlled with phase control. A TRIAC can be used for simple on/off control of an AC motor though, as long as it can handle the current surge, when it's turned on and snubber is added to damp the turn off voltage spike.