The bit about eliminating chimneys is that you can use a TEG to power a fan which gets the smoke out, instead of relying on convection, which needs a chimney, and many impoverished places lack the means to make holes in roofs. A properly designed chimney absorbs and stores a considerable portion of the heat flowing through it.

Also not sure about the max temperature these things can handle. They mention that the benefit of using these between a heat source and water that is being heated is that the water keeps the element from getting too hot.