madison said:I can attest that a cast iron kettle placed directly on a steel stove top will boil hard enough to spit water out the spout like a whale, and when that water hits the stove top, it will wake you out of a deep sleep.
Use a cast pot rather than a kettle - no spout for spitting, and a lot more surface area for evaporation. If you are getting a hard boil, use a tile or trivet.
Not sure why, but the water in my cast iron pot never seems to bubble or boil, it just steams (and goes through as much as a few gallons a day). But I can easily bring water to a boil in my steel tea kettle.