We bought two from Big Als...when we got them, we noticed that on the box it said Not submersible. We called Big Als, thinking that maybe they sent us the wrong heater. Not so, apparently in canada, they are not allowed to sell submersible heaters because it violates their safety codes.
They told us the heaters were submersible, but we got boxes that were labeled for canada and not the u.s.. The line is actually a do not go below this line, but for canada. The same heaters go in both boxes, just the messaging is different.