As long as you have an air stone or a power head pointing up near the top of the tank then you can turn up the heater quite high and it will be beneficial.
It's mentioned in the fishless cycling thread which you should definitely read before doing your cycle: http/www.fishforums.net/index.php?showtopic=113861
if you are wondering if it will damage the heater or not, im pretty sure it wont as long as you dont dump the whole bottle in there and if you do dump the whole thing in there, i would say fish keeping isnt for you