The opening lines immediately reminded me of this wonderful article about old technology behind energy efficient brick ovens:

https://web.archive.org/web/20140327025219/http://www.lowtec...

(waybackmachine because the official website is down).

There's surprisingly many old and forgotten technologies that are still relevant in terms of energy efficiency. Of course, this particular one is only relevent at industrial scales, but the website has more articles to offer.