Step 1: What is the heating load of your building?
It's not possible to estimate your wood consumption, without knowing the average heat demand of your building is. This is called the heating load, most often estimated on the basis of heated room area, but preferably done by a profesional.
STEP 2. How much wood has to burned on a daily base?
Once you know your heating load, you can determine how much wood that needs to be burned an a daily base. Seasoned fire wood (Red Oak) has around 8,550 BTU/Lb heating value on a dry base. So let's assume your heating load is 500,000 BTU per day. You need 500,000 / 8,550 equals 58.5 Lbs of Red Oak fire wood. With a 20% moisture content this becomes 73 Lbs of Red Oak fire wood.
For some people it wouldn't be a problem to stoke their wood boiler with up to 73 Lbs of fire wood every day, whereas for busy professionals and hard working people it would be almost impossible to find time for this. Because the heating load is related to outdoor ambient temperatures between 10°F and 3°F (-12°C and -16°C), it always refers to the maximal heat demand of the building. However, during the cold winter season, up to 60% of the days usually are having an milder average outdoor temperature of between -5°C and 5°C (23°F and 41°F). In this case, the actual demand is around 30-50% below the expected peak value. Therefore it is advised to distinguish between a normal winter day and the theoretical peak demand.
The amount of wood to be burned every day has a practical limit, determining the applicability of the use of an indoor wood boiler as the only central heating source. First, if the wood boiler will be stoked manually without water storage, the maximal heating load of the building should not exceed 40,000 BTU/Hr (12 kW). More heat can be delivered only by continuous burning and the use of water storage, to a maximum of approx. 80,000 BTU/Hr (24 kW).
STEP 3. What is your estimated annual wood consumption?