Well, you guys have me quite curious. So I hooked the mini piezo buzzer I had up to the scope. And if I cause air to whistle through it, I can get up to about 500 mV. That was about the peak for my mini piezo though.

Then after reading your post about thermo electric, I pulled out one of my peltier devices. Mine has heat sinks on both sides, so you may be able to generate more electricity with just a bare peltier using this method. I was able to get to about 1.025 Volts using hot tap water in a Ziploc ® one side, and an ice pack on the other. Total guess of about 100 degrees difference. I was sort of hoping to see a little more volts out of this one.

Walter