Well, upon further investigation, it appears that my sump isn't deep/wide enough to fully submerge the heater. How much of the heater must be in the water? I don't have anything in the tank now, so I suppose I could just play with it to find out if it will heat properly or not. Just wondering if yours goes all the way in...
Wow, so many "that's what she said" lines in that paragraph.
Most heaters are designed to be fully submerged. Evaporation is going to cause the water level to get lower and lower and if you start out with some of it exposed, chances are one of these days you might find an overly-exposed heater that's fried or cracked.
Ahh, so physical damage to the heater is a worry. Then I'll just leave it in the tank. It's a definitely meant to be fully submerged, because it is now, but I'm not sure what brand/model at the moment.
Eh, well I live in Florida. I'm not too concerned with it getting too cold. I have the heater all the way down... it's December... and the water is 79 degrees. Guess I'll be looking at a Carribbean species