I ended up using a crock pot for my heater. I hooked it to one of the timed outlet switches (like people use on lamps, while on vacation). On for 30min, off for 30min. I figured that would keep the mix nice and warm, without actually cooking anything. Next time, I may try for on 30min, and off 1 hour. The water definitely got hot to the touch (not just warm). To the point of unpleasantness. Overall, though, seemed to work good.