Okay so I bought one to try it out, since Fihsboy said they were very accurate. I fully submerged it when I got it but looked at it closely and it says not to submerge past the water line on it. I poured over the internet and concluded that because of the UL listing they have to say don't submerge past the water line. People say they submerge them and have submerged them for years. However, I had mine submerged for about 2 hours and it is set to 78 and the temp is now fluctuating between 80-80.9 so far. I unplugged it, took it out of the sump and put it into the overflow vertically. The thing is set to 78, my temp is 80, and the stupid thing is still heating the tank. I have had this heater for less than 3 hours in my tank. What the F@#%!!!!!!!!!!!!

Thinking about sending it back to fosterandsmith and getting a rena smart heater. They are out of stock though, so I guess I'll have to wait. Hopefully this heater will balance itself out maybe. It's staying around 80.5 average.

yeah, i just told foster and smith to ship me a return label and a new heater, only had to pay $8 for the extra heater price. It a Via Aqua Titanium "actual submersible" heater with the temp control on the chord. You will be hearing my reviews in about a week, haha. I also told them to never ship my stuff through fedex post. It takes an extra 3-4 days... Stupid..

its all cool, foster and smith was pretty nice about it. i was ready to chew them out, haha. i mean, it took 8 days to get here, then the thing doesnt work right from the box. well, im glad you heard good things about the heater i'll be getting. the external temp dial is gonna be the greatest thing in the world, haha. they make the damn dials soo hard to turn. ahah.