There is probably still a lot out there but with the current state of the ('free') search engines you won't find much. I am painfully reminded of that every time I have to look for a datasheet that is not in my own archive yet.
The damage from a frozen water line in your house can be a lot more than $4000.
We had them when I was still a kid in the sixties and I did not like it at all. Jumping in a warm bed is nice but leaving it on during the night makes you wake up all sweaty in the middle of the night. Even on the lowest setting.