Firewood

[Dan Howard]

Apparently evidence of coppicing has been found dating back to the Neolithic period. An acre of 20 year-old native woodland might produce 20-25 cords of usable timber. Coppicing can more than double this yield - depending on the species. Coppice timber was actually preferred by the charcoal makers because it was of regular size, easy to handle and load, and required minimal trimming

[Arahne]

Two articles that could be of interest for this topic:

A note about the use of coal in the Roman Britain, Antiquaries Journal, XXXV-2, 1955.
Heizversuch an einer rekonstruirten Kanal Heizung, Saalburg Jahrbuch XXXVI, 1979.
In the second one, experiment shows that 30 kg's of wood are needed for achieving proper temperature in the room of 25 sqm during the cold weather.