thermal mass of rock directly upon stove holds and radiates heat

Advances in heating:  thermal mass of rock directly upon stove holds and radiates heat from stoves much much more efficiently than without using rock or by just having rock a foot away from stove.   Best rock to use is dense rounded river rock as it is unlikely to explode or crack due to bubbles in rock since the river-tumbling has eliminated rocks with much air bubble in them.
One may also use same rock heated on gas stove or gas oven or wood stove--put into wool sock and use.

in the bottom picture this is for hot-water bathing at left as well as for tremendous radiant heat

There are other ideas such as conducting either the hot flue-air back and forth through rock or thermal mass or conducting heated water through flooring, etc.
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SEE THIS:    11-22-17   https://www.express.co.uk/news/politics/882881/Brexit-EU-secret-document-truth-British-public