The gap between the double walls should be filled up with heat transfer liquid. Some may use water for this purpose, but water can not be heated over 100 Celsius at normal pressure. If you want to collect the most alcohol out of your wash, heat transfer oils are needed, as they can heat your wash far over 100 Celsius.
Approximate quantities of heat transfer oil needed for different sized distillers:
- 10l double walled distiller: 3l
- 20l double walled distiller: 4l
- 30l double walled distiller: 6l
- 40l double walled distiller: 7l
- 50l double walled distiller: 9l
- 80l double walled distiller: 15l
- 100l double walled distiller: 18l