NOTE:-industry is having to pay a carbon tax on heating oil, but horticulture is having a temporary reprieve.

To calculate your maximum heat requirement.
Area of walls + roof (Sq. M) x 0.0008 factor x temperature lift (degrees C.)
= Total (Kilowatts/hour).

The temperature lift required will depend on whether you need real heat or only frost protection.

To calculate the average heat requirement.
Over a period of time the average heat requirement will be about 30% of the maximum heat requirement; therefore... Total (from above) x 0.3

To calculate the Kilowatts per load.
Multiply the average heat requirement by the number of hours between loading.

How much fuel?
1Kg of dry wood and most other bio-mass fuels will yield 5Kw of energy. Divide your kilowatts per load by 5 to give the kilogrammes per load. Now refer to the table and choose the most suitable model.