In the colder parts of Spain, some villages still have houses with an ancient underfloor heating system known as a 'gloria'. The fire would be lit once a day and when it was burning well the firebox would be covered to slow the burning rate and keep the heat inside.
"The warm exhaust gases from the combustion heat are led through one or more ducts that run under the floor of the heated room(s), and then rise through the chimney. The floor and the walls slowly radiate this heat into the room. In summer, a natural air current in the gloria cools the room(s)."
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