Tom Mazanec has started "a new series of blog posts called Sidestreets."

These are the extraneous historical and cultural details that I come across on a daily basis but contribute nothing to the arguments I develop in my research. They are the shiny little nuggets of ordinary rock that are sifted out when you pan for gold. They are all the roads not taken because they probably lead to dead ends.

The first post is about "ash animals." I realized after posting my comment there that these turn up in the (ca 1000 CE) Wakan Rōeishū 和漢朗詠集 too, in a Chinese poem in the "Fireplace" (炉火) section by Sugawara no Sukeaki 菅原輔昭, one of the Thirty-Six Heian-era Immortals of Poetry (中古三十六歌仙, not to be confused with the original Thirty-six Immortals of Poetry):

多時縱酔鴬花下。近日那離獣炭辺。
I may have been drunk beneath the nightingales and flowers on many occasions/ But how could I depart from my place by the ash animal these days?

The ash-animal here is understood not just to be for warmth, but also for warming up drinks. (Side-note: Given the Japanese reading sumi, in Japan at least they were probably understood to be made of charcoal rather than ash, but I'll stick with Tom's terminology.) Kōda Toshio 甲田利雄's 1987 edition of the Gōdanshō, which also contains this poem, includes a note alongside it (p 413): "獣炭羊琇所作也". This more or less means "Ash animals: as made by Yáng Xiù", explicitly linking this poem to precisely the criticisms of Yáng mentioned by Tom. Not to make a point about inequality, mind you — just so that we realize that Sugawara is actually heating up some booze in the second line there. (The WR was a collection of poems to be sung by the literate elite of Heian Japan — not a group overburdened with egalitarian ideals.)

In other words: as much as he enjoyed drinking outside in spring, by winter Sugawara was a slave to the ash animal. Pretty much the kotatsu of Heian Japan, then.