Heating a Small House on Gathered Wood: The Heat-Loss Budget, the Kilograms per Day, and the Hours of Gathering a Winter Actually Costs

A household that heats with wood it gathers itself does not pay for warmth in money; it pays in kilograms and in hours. This paper computes both currencies for one plainly specified dwelling: a single-storey house of 40 square metres floor area, built to modest, older construction standards, held at 18 degrees Celsius through a 150-day winter whose mean outdoor temperature is 0 degrees Celsius and whose coldest design night reaches minus 15 degrees Celsius. The steady-state heat-loss coefficient of the house is 127.0 watts per kelvin, of which the walls contribute 34.2, the floor 28.0, ventilation 26.4, the windows and door 22.4, and the roof 16.0 watts per kelvin. On the design day the house needs 100.58 kilowatt-hours of heat, which is 38.69 kilograms of air-dry wood through a stove of 65 percent efficiency, or 1.55 hours of gathering work at 25 kilograms per person-hour. On an average winter day the figures are 54.86 kilowatt-hours, 21.10 kilograms, and 0.84 hours. Across the whole season the house consumes 3,165 kilograms of wood — 3.165 tonnes — and 126.61 hours of gathering, cutting, splitting, and stacking: roughly sixteen eight-hour working days spent feeding one small house. Of five single fabric improvements tested one at a time, insulating the walls from a U-value of 0.60 to 0.25 watts per square metre per kelvin buys back the most labour, 19.89 gathering hours per winter, followed by floor insulation at 15.95 hours and draught sealing at 13.16 hours. The ranking is the practical result: for a household poor in time rather than money, improvements should be bought in the order that returns hours, and the walls come first.