I recently stumbled upon a publication by the Freiluftlabor Lauresham (laboratory for experimental archaeology) at Lorsch in Germany. They measured living conditions (temperature, humidity, carbon monoxide concentrations, etc…) in a reconstructed house of the Carolingian period while it was inhabited by 4-8 people over a period of multiple days in winter. The house measures 10.8m by 5.4m, has walls of wattle and daub and a roof covering of thatch. There are two open fireplaces that were stoked using wood from deciduous trees and andirons were used to guarantee smokeless fire.

For heating alone, they used an average of 45kg wood per day. Additionally, 17kg of wood per day were used for cooking. This is in line with measurements of similar experiments in a Danish open-air museum where they used 39-55kg/day in a reconstructed house of the viking age and 74kg/day in a reconstruction of an iron age house.

Interestingly, despite the high amounts of wood being burned the room temperatures were generally only around 4 degrees Celsius higher than outside temperatures.

To estimate the total amount of wood used during a year they assumed that fires for heating would be lit on days with temperatures below 10 degrees Celsius, around 174 days a year in this particular region.

In summary, a small house inhabited by 4-8 persons in the 9th century, situated in a region of mild climate in Germany, might have used as much as 7.8t of firewood for heating in a year and an additional 6.2t for cooking.