[rahtreelimbs]

I heard that keeping your frequency low puts more heat into the metal than having the frequency high.

Is this true and if so how is this happening?

[Oscar]

Yea it does have that effect. This is because there are fewer crossings of the 0V point with a lower AC frequency. No "square wave" is an actual perfect square wave, and will ultimately have a certain slope (as opposed to an un-defined slope where the "line" is perfectly vertical) as it switches polarity. During the brief time it slopes up/down the heat delivered is less than what is delivered when the waveform is at the peak.

[MinnesotaDave]

In my understanding it's true.

Think of higher frequency meaning more of the zero crossing points - cross enough times and the net effect should be less overall amperage getting to the metal.

Edit: I see Oscar got ya covered