David Turner,
The toaster does it's part in heat exchange. On a cold morning it it does a little to warm the kitchen and it is a nice hand-warmer as well all the while making toast.
While heat exchange things might be economically possible they also might be practically and aesthetically undesirable, like toasting bagels in a toaster. Somethings are done and have a bad taste and somethings are done in bad taste.
Michael.hill, we use the open-top flat-bed toaster (as described in my previous comments) for bagels, they are just too thick to fit in the toaster, too easy to get caught in it's works, and really, just one side is desired to be toasted.
The denizens of Macbethland's north have the right idea for bread products of all types, they do not worry about fat exchange more than heat exchange, it suits them well to just fry their bread in a sizzling puddle of sausage fat.