Depending on the size of the tank, maybe they could just lower the heater a little bit? But yes, lowering it is a good idea. If it's near a window and getting a slight cold breeze or anything, do keep this in mind and do something like wrap a towel around the side that is affected most.
I did this when I was in my school's dorms and it was *very* effective against that cold, really insulates it a lot. I'd imagine that the heater will be off for the most part in your house as well, it may just be best to wrap a towel or two around the whole tank to help it insulate.