I think it would heat the water, but wouldnt you always have to moniter the temperature so it doesn't get to high or too low? I just don't see how that would work.
That's what I'm finding. I know they make products call rheostats (spelling?) that basically turn the fixture off and on if it falls outside of the range you want. But if I'd go that route, I'd just assume pay for a normal heater lol.