I didn't see anyone mention the reason this whole thing about not putting hot foods in the refrigerator got started in the first place.
Back before there were refrigerators, there were iceboxes. Put hot food in an icebox, the ice melts more quickly, and if the ice melts too quickly, all the food in the icebox may go bad before the iceman comes around to deliver another block. So food had to be left to cool before it could go in the icebox.
Even then, much as now, there were people who didn't bother to wonder
why they shouldn't put hot food in the icebox, they just knew they weren't supposed to. I know, it may seem obvious, but then, a lot of things do, don't they?
Fast-forward a few years, and envision little Sally asking her mother why she shouldn't put hot food in the refrigerator, and her mother telling her "You just shouldn't." Or, another one I heard once: "Because it will go sour." Whatever that means. It's just a carry-over from the icebox days, something their mother or grandmother taught them, which is no longer valid because of new technology. Of course, you still shouldn't park a giant red-hot cauldron of chili right up against your milk. And because heat rises, it is a good idea to put hot foods on the top shelf; if put on the bottom, they will be heating everything above them. Oh, and never put a ceramic container, like the liner of your crock pot, for instance, in the refrigerator while it is still hot; it will most likely break.
The bit about food going "sour," by the way, was from an old girlfriend, whose mother had apparently been full of cooking myths and quite devoid of logic. She would invariably throw out partial cans of olives and anything else like that that I neglected to put in other containers. Though when asked why, she didn't really know. "You just can't store things in cans in the refrigerator," she would say, while looking at me as though my foolishness would eventually poison us both.
That myth, I'm sure, grew out of a misguided fear of botulism. Not that the fear of botulism is misguided, but the fear of the method by which it might be contracted. Any canned food stored on a shelf that bursts or is otherwise breached needs to be thrown out due to the near certainty of botulism, but that simply does not apply to intact canned goods that are opened, partially used, then refrigerated. If it did, we'd have to re-package ketchup, once we opened it.