A centrifugal fan is essential for running a downdraught gasifier. However, searching for a fan can almost be impossible or too expensive if you are lucky enough to find one. After purchasing How to Design and Build Centrifugal Fans enough information is at hand to build a fan from scrap materials.
In the picture below we can see one side of a fan cut out of a piece of plywood. The correct dimensions for the fan required are taken from the book.
In the next picture we can see two plywood framing pieces cut out for both sides of the fan. Below the framing pieces a sheet of light gauge steel has been cut from a vegetable oil can that will act as a shield to protect the plywood.